diff --git a/.clang-format b/.clang-format
index b80d2c6..78696f5 100644
--- a/.clang-format
+++ b/.clang-format
@@ -16,6 +16,6 @@ AllowShortLoopsOnASingleLine: true
 
 PointerAlignment: Left
 AlignConsecutiveAssignments: false
-AlignTrailingComments: false
+AlignTrailingComments: true
 
 SpaceAfterCStyleCast: true
diff --git a/README.md b/README.md
index 35e93e4..3c440c2 100644
--- a/README.md
+++ b/README.md
@@ -14,6 +14,9 @@ it is simplest to just include [gsl.h](./include/gsl.h) and gain access to the e
 > NOTE: We encourage contributions that improve or refine any of the types in this library as well as ports to
 other platforms. Please see [CONTRIBUTING.md](./CONTRIBUTING.md) for more information about contributing.
 
+# Project Code of Conduct
+This project has adopted the [Microsoft Open Source Code of Conduct](https://opensource.microsoft.com/codeofconduct/). For more information see the [Code of Conduct FAQ](https://opensource.microsoft.com/codeofconduct/faq/) or contact [opencode@microsoft.com](mailto:opencode@microsoft.com) with any additional questions or comments.
+
 # Quick Start
 ## Supported Platforms
 The test suite that exercises GSL has been built and passes successfully on the following platforms:
diff --git a/include/gsl.h b/include/gsl.h
index ad064ba..8e00a44 100644
--- a/include/gsl.h
+++ b/include/gsl.h
@@ -1,17 +1,17 @@
-/////////////////////////////////////////////////////////////////////////////// 
-// 
-// Copyright (c) 2015 Microsoft Corporation. All rights reserved. 
-// 
-// This code is licensed under the MIT License (MIT). 
-// 
-// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 
-// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 
-// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE 
-// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 
-// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, 
-// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN 
-// THE SOFTWARE. 
-// 
+///////////////////////////////////////////////////////////////////////////////
+//
+// Copyright (c) 2015 Microsoft Corporation. All rights reserved.
+//
+// This code is licensed under the MIT License (MIT).
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+//
 ///////////////////////////////////////////////////////////////////////////////
 
 #pragma once
@@ -21,36 +21,36 @@
 
 #include "gsl_assert.h"  // Ensures/Expects
 #include "gsl_util.h"    // finally()/narrow()/narrow_cast()...
-#include "span.h"           // span, strided_span...
-#include "string_span.h"    // zstring, string_span, zstring_builder...
+#include "multi_span.h"  // multi_span, strided_span...
+#include "span.h"        // span
+#include "string_span.h" // zstring, string_span, zstring_builder...
 #include <memory>
 
 #ifdef _MSC_VER
 
 // No MSVC does constexpr fully yet
 #pragma push_macro("constexpr")
-#define constexpr 
+#define constexpr
 
 // MSVC 2013 workarounds
 #if _MSC_VER <= 1800
-// noexcept is not understood 
+// noexcept is not understood
 #pragma push_macro("noexcept")
-#define noexcept  
+#define noexcept
 
 // turn off some misguided warnings
 #pragma warning(push)
-#pragma warning(disable: 4351) // warns about newly introduced aggregate initializer behavior
+#pragma warning(disable : 4351) // warns about newly introduced aggregate initializer behavior
 
 #endif // _MSC_VER <= 1800
 
 #endif // _MSC_VER
 
-
 namespace gsl
 {
 
 //
-// GSL.owner: ownership pointers 
+// GSL.owner: ownership pointers
 //
 using std::unique_ptr;
 using std::shared_ptr;
@@ -58,67 +58,74 @@ using std::shared_ptr;
 template <class T>
 using owner = T;
 
-
 //
 // not_null
 //
 // Restricts a pointer or smart pointer to only hold non-null values.
-// 
+//
 // Has zero size overhead over T.
 //
-// If T is a pointer (i.e. T == U*) then 
-// - allow construction from U* or U& 
+// If T is a pointer (i.e. T == U*) then
+// - allow construction from U* or U&
 // - disallow construction from nullptr_t
 // - disallow default construction
 // - ensure construction from U* fails with nullptr
 // - allow implicit conversion to U*
 //
-template<class T>
+template <class T>
 class not_null
 {
     static_assert(std::is_assignable<T&, std::nullptr_t>::value, "T cannot be assigned nullptr.");
+
 public:
     not_null(T t) : ptr_(t) { ensure_invariant(); }
-    not_null& operator=(const T& t) { ptr_ = t; ensure_invariant(); return *this; }
+    not_null& operator=(const T& t)
+    {
+        ptr_ = t;
+        ensure_invariant();
+        return *this;
+    }
 
-    not_null(const not_null &other) = default;
-    not_null& operator=(const not_null &other) = default;
+    not_null(const not_null& other) = default;
+    not_null& operator=(const not_null& other) = default;
 
     template <typename U, typename Dummy = std::enable_if_t<std::is_convertible<U, T>::value>>
-    not_null(const not_null<U> &other)
+    not_null(const not_null<U>& other)
     {
         *this = other;
     }
 
     template <typename U, typename Dummy = std::enable_if_t<std::is_convertible<U, T>::value>>
-    not_null& operator=(const not_null<U> &other)
+    not_null& operator=(const not_null<U>& other)
     {
         ptr_ = other.get();
         return *this;
     }
 
-    // prevents compilation when someone attempts to assign a nullptr 
+    // prevents compilation when someone attempts to assign a nullptr
     not_null(std::nullptr_t) = delete;
     not_null(int) = delete;
     not_null<T>& operator=(std::nullptr_t) = delete;
-	not_null<T>& operator=(int) = delete;
-    
-    T get() const {
+    not_null<T>& operator=(int) = delete;
+
+    T get() const
+    {
 #ifdef _MSC_VER
         __assume(ptr_ != nullptr);
 #endif
         return ptr_;
     } // the assume() should help the optimizer
 
-    operator T() const {  return get(); }
+    operator T() const { return get(); }
     T operator->() const { return get(); }
 
-	bool operator==(const T& rhs) const { return ptr_ == rhs; }
-	bool operator!=(const T& rhs) const { return !(*this == rhs); }
+    bool operator==(const T& rhs) const { return ptr_ == rhs; }
+    bool operator!=(const T& rhs) const { return !(*this == rhs); }
 private:
     T ptr_;
 
-    // we assume that the compiler can hoist/prove away most of the checks inlined from this function
+    // we assume that the compiler can hoist/prove away most of the checks inlined from this
+    // function
     // if not, we could make them optional via conditional compilation
     void ensure_invariant() const { Expects(ptr_ != nullptr); }
 
@@ -138,14 +145,11 @@ private:
 
 namespace std
 {
-    template<class T>
-    struct hash<gsl::not_null<T>>
-    {
-        size_t operator()(const gsl::not_null<T> & value) const
-        {
-            return hash<T>{}(value);
-        }
-    };
+template <class T>
+struct hash<gsl::not_null<T>>
+{
+    size_t operator()(const gsl::not_null<T>& value) const { return hash<T>{}(value); }
+};
 
 } // namespace std
 
@@ -158,7 +162,7 @@ namespace std
 
 #undef noexcept
 #pragma pop_macro("noexcept")
- 
+
 #pragma warning(pop)
 
 #endif // _MSC_VER <= 1800
diff --git a/include/gsl_assert.h b/include/gsl_assert.h
index 51e8ab6..10de31a 100644
--- a/include/gsl_assert.h
+++ b/include/gsl_assert.h
@@ -1,17 +1,17 @@
-/////////////////////////////////////////////////////////////////////////////// 
-// 
-// Copyright (c) 2015 Microsoft Corporation. All rights reserved. 
-// 
-// This code is licensed under the MIT License (MIT). 
-// 
-// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 
-// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 
-// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE 
-// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 
-// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, 
-// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN 
-// THE SOFTWARE. 
-// 
+///////////////////////////////////////////////////////////////////////////////
+//
+// Copyright (c) 2015 Microsoft Corporation. All rights reserved.
+//
+// This code is licensed under the MIT License (MIT).
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+//
 ///////////////////////////////////////////////////////////////////////////////
 
 #pragma once
@@ -28,50 +28,50 @@
 //
 // 1. GSL_TERMINATE_ON_CONTRACT_VIOLATION: std::terminate will be called (default)
 // 2. GSL_THROW_ON_CONTRACT_VIOLATION: a gsl::fail_fast exception will be thrown
-// 3. GSL_UNENFORCED_ON_CONTRACT_VIOLATION: nothing happens  
+// 3. GSL_UNENFORCED_ON_CONTRACT_VIOLATION: nothing happens
 //
-#if !(defined(GSL_THROW_ON_CONTRACT_VIOLATION) ^ defined(GSL_TERMINATE_ON_CONTRACT_VIOLATION) ^ defined(GSL_UNENFORCED_ON_CONTRACT_VIOLATION))
-#define GSL_TERMINATE_ON_CONTRACT_VIOLATION 
+#if !(defined(GSL_THROW_ON_CONTRACT_VIOLATION) ^ defined(GSL_TERMINATE_ON_CONTRACT_VIOLATION) ^    \
+      defined(GSL_UNENFORCED_ON_CONTRACT_VIOLATION))
+#define GSL_TERMINATE_ON_CONTRACT_VIOLATION
 #endif
 
-
 #define GSL_STRINGIFY_DETAIL(x) #x
 #define GSL_STRINGIFY(x) GSL_STRINGIFY_DETAIL(x)
 
-
 //
 // GSL.assert: assertions
 //
 
 namespace gsl
 {
-struct fail_fast : public std::runtime_error 
+struct fail_fast : public std::runtime_error
 {
-	explicit fail_fast(char const* const message) : std::runtime_error(message) {}   
+    explicit fail_fast(char const* const message) : std::runtime_error(message) {}
 };
 }
 
 #if defined(GSL_THROW_ON_CONTRACT_VIOLATION)
 
-#define Expects(cond)  if (!(cond)) \
-    throw gsl::fail_fast("GSL: Precondition failure at " __FILE__ ": " GSL_STRINGIFY(__LINE__));
-#define Ensures(cond)  if (!(cond)) \
-    throw gsl::fail_fast("GSL: Postcondition failure at " __FILE__ ": " GSL_STRINGIFY(__LINE__));
-
+#define Expects(cond)                                                                              \
+    if (!(cond))                                                                                   \
+        throw gsl::fail_fast("GSL: Precondition failure at " __FILE__ ": " GSL_STRINGIFY(__LINE__));
+#define Ensures(cond)                                                                              \
+    if (!(cond))                                                                                   \
+        throw gsl::fail_fast("GSL: Postcondition failure at " __FILE__                             \
+                             ": " GSL_STRINGIFY(__LINE__));
 
 #elif defined(GSL_TERMINATE_ON_CONTRACT_VIOLATION)
 
-
-#define Expects(cond)           if (!(cond)) std::terminate(); 
-#define Ensures(cond)           if (!(cond)) std::terminate();
-
+#define Expects(cond)                                                                              \
+    if (!(cond)) std::terminate();
+#define Ensures(cond)                                                                              \
+    if (!(cond)) std::terminate();
 
 #elif defined(GSL_UNENFORCED_ON_CONTRACT_VIOLATION)
 
-#define Expects(cond)           
-#define Ensures(cond)           
-
-#endif 
+#define Expects(cond)
+#define Ensures(cond)
 
+#endif
 
 #endif // GSL_CONTRACTS_H
diff --git a/include/gsl_byte.h b/include/gsl_byte.h
new file mode 100644
index 0000000..5a9c327
--- /dev/null
+++ b/include/gsl_byte.h
@@ -0,0 +1,125 @@
+///////////////////////////////////////////////////////////////////////////////
+//
+// Copyright (c) 2015 Microsoft Corporation. All rights reserved.
+//
+// This code is licensed under the MIT License (MIT).
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+//
+///////////////////////////////////////////////////////////////////////////////
+
+#pragma once
+
+#ifndef GSL_BYTE_H
+#define GSL_BYTE_H
+
+#ifdef _MSC_VER
+
+// MSVC 2013 workarounds
+#if _MSC_VER <= 1800
+
+// constexpr is not understood
+#pragma push_macro("constexpr")
+#define constexpr
+
+// noexcept is not understood
+#pragma push_macro("noexcept")
+#define noexcept
+
+#endif // _MSC_VER <= 1800
+
+#endif // _MSC_VER
+
+namespace gsl
+{
+// This is a simple definition for now that allows
+// use of byte within span<> to be standards-compliant
+enum class byte : unsigned char
+{
+};
+
+template <class IntegerType, class = std::enable_if_t<std::is_integral<IntegerType>::value>>
+constexpr byte& operator<<=(byte& b, IntegerType shift) noexcept
+{
+    return b = byte(static_cast<unsigned char>(b) << shift);
+}
+
+template <class IntegerType, class = std::enable_if_t<std::is_integral<IntegerType>::value>>
+constexpr byte operator<<(byte b, IntegerType shift) noexcept
+{
+    return byte(static_cast<unsigned char>(b) << shift);
+}
+
+template <class IntegerType, class = std::enable_if_t<std::is_integral<IntegerType>::value>>
+constexpr byte& operator>>=(byte& b, IntegerType shift) noexcept
+{
+    return b = byte(static_cast<unsigned char>(b) >> shift);
+}
+
+template <class IntegerType, class = std::enable_if_t<std::is_integral<IntegerType>::value>>
+constexpr byte operator>>(byte b, IntegerType shift) noexcept
+{
+    return byte(static_cast<unsigned char>(b) >> shift);
+}
+
+constexpr byte& operator|=(byte& l, byte r) noexcept
+{
+    return l = byte(static_cast<unsigned char>(l) | static_cast<unsigned char>(r));
+}
+
+constexpr byte operator|(byte l, byte r) noexcept
+{
+    return byte(static_cast<unsigned char>(l) + static_cast<unsigned char>(r));
+}
+
+constexpr byte& operator&=(byte& l, byte r) noexcept
+{
+    return l = byte(static_cast<unsigned char>(l) & static_cast<unsigned char>(r));
+}
+
+constexpr byte operator&(byte l, byte r) noexcept
+{
+    return byte(static_cast<unsigned char>(l) & static_cast<unsigned char>(r));
+}
+
+constexpr byte& operator^=(byte& l, byte r) noexcept
+{
+    return l = byte(static_cast<unsigned char>(l) ^ static_cast<unsigned char>(r));
+}
+
+constexpr byte operator^(byte l, byte r) noexcept
+{
+    return byte(static_cast<unsigned char>(l) ^ static_cast<unsigned char>(r));
+}
+
+constexpr byte operator~(byte b) noexcept { return byte(~static_cast<unsigned char>(b)); }
+
+template <class IntegerType, class = std::enable_if_t<std::is_integral<IntegerType>::value>>
+constexpr IntegerType to_integer(byte b) noexcept
+{
+    return {b};
+}
+
+} // namespace gsl
+
+#ifdef _MSC_VER
+
+#if _MSC_VER <= 1800
+
+#undef constexpr
+#pragma pop_macro("constexpr")
+
+#undef noexcept
+#pragma pop_macro("noexcept")
+
+#endif // _MSC_VER <= 1800
+
+#endif // _MSC_VER
+
+#endif // GSL_BYTE_H
\ No newline at end of file
diff --git a/include/gsl_util.h b/include/gsl_util.h
index b42b66a..92a795b 100644
--- a/include/gsl_util.h
+++ b/include/gsl_util.h
@@ -19,11 +19,11 @@
 #ifndef GSL_UTIL_H
 #define GSL_UTIL_H
 
-#include "gsl_assert.h"  // Ensures/Expects
+#include "gsl_assert.h" // Ensures/Expects
 #include <array>
-#include <utility>
-#include <type_traits>
 #include <exception>
+#include <type_traits>
+#include <utility>
 
 #ifdef _MSC_VER
 
@@ -32,7 +32,7 @@
 #define constexpr
 
 #pragma warning(push)
-#pragma warning(disable: 4127) // conditional expression is constant
+#pragma warning(disable : 4127) // conditional expression is constant
 
 // MSVC 2013 workarounds
 #if _MSC_VER <= 1800
@@ -42,13 +42,12 @@
 
 // turn off some misguided warnings
 #pragma warning(push)
-#pragma warning(disable: 4351) // warns about newly introduced aggregate initializer behavior
+#pragma warning(disable : 4351) // warns about newly introduced aggregate initializer behavior
 
 #endif // _MSC_VER <= 1800
 
 #endif // _MSC_VER
 
-
 namespace gsl
 {
 //
@@ -60,18 +59,20 @@ template <class F>
 class final_act
 {
 public:
-    explicit final_act(F f) noexcept
-    : f_(std::move(f)), invoke_(true)
-    {}
+    explicit final_act(F f) noexcept : f_(std::move(f)), invoke_(true) {}
 
-    final_act(final_act&& other) noexcept
-    : f_(std::move(other.f_)), invoke_(other.invoke_)
-    { other.invoke_ = false; }
+    final_act(final_act&& other) noexcept : f_(std::move(other.f_)), invoke_(other.invoke_)
+    {
+        other.invoke_ = false;
+    }
 
     final_act(const final_act&) = delete;
     final_act& operator=(const final_act&) = delete;
 
-    ~final_act() noexcept { if (invoke_) f_(); }
+    ~final_act() noexcept
+    {
+        if (invoke_) f_();
+    }
 
 private:
     F f_;
@@ -80,34 +81,43 @@ private:
 
 // finally() - convenience function to generate a final_act
 template <class F>
-inline final_act<F> finally(const F &f)
-noexcept { return final_act<F>(f); }
+inline final_act<F> finally(const F& f) noexcept
+{
+    return final_act<F>(f);
+}
 
 template <class F>
-inline final_act<F> finally(F &&f) noexcept
-{ return final_act<F>(std::forward<F>(f)); }
+inline final_act<F> finally(F&& f) noexcept
+{
+    return final_act<F>(std::forward<F>(f));
+}
 
 // narrow_cast(): a searchable way to do narrowing casts of values
-template<class T, class U>
+template <class T, class U>
 inline constexpr T narrow_cast(U u) noexcept
-{ return static_cast<T>(u); }
+{
+    return static_cast<T>(u);
+}
 
-struct narrowing_error : public std::exception {};
+struct narrowing_error : public std::exception
+{
+};
 
 namespace details
 {
-    template<class T, class U>
-    struct is_same_signedness : public std::integral_constant<bool, std::is_signed<T>::value == std::is_signed<U>::value>
-    {};
+    template <class T, class U>
+    struct is_same_signedness
+        : public std::integral_constant<bool, std::is_signed<T>::value == std::is_signed<U>::value>
+    {
+    };
 }
 
 // narrow() : a checked version of narrow_cast() that throws if the cast changed the value
-template<class T, class U>
+template <class T, class U>
 inline T narrow(U u)
 {
     T t = narrow_cast<T>(u);
-    if (static_cast<U>(t) != u)
-        throw narrowing_error();
+    if (static_cast<U>(t) != u) throw narrowing_error();
     if (!details::is_same_signedness<T, U>::value && ((t < T{}) != (u < U{})))
         throw narrowing_error();
     return t;
@@ -117,24 +127,35 @@ inline T narrow(U u)
 // at() - Bounds-checked way of accessing static arrays, std::array, std::vector
 //
 template <class T, size_t N>
-constexpr T& at(T(&arr)[N], size_t index)
-{ Expects(index < N); return arr[index]; }
+constexpr T& at(T (&arr)[N], size_t index)
+{
+    Expects(index < N);
+    return arr[index];
+}
 
 template <class T, size_t N>
 constexpr T& at(std::array<T, N>& arr, size_t index)
-{ Expects(index < N); return arr[index]; }
+{
+    Expects(index < N);
+    return arr[index];
+}
 
 template <class Cont>
 constexpr typename Cont::value_type& at(Cont& cont, size_t index)
-{ Expects(index < cont.size()); return cont[index]; }
+{
+    Expects(index < cont.size());
+    return cont[index];
+}
 
 template <class T>
 constexpr const T& at(std::initializer_list<T> cont, size_t index)
-{ Expects(index < cont.size()); return *(cont.begin() + index); }
+{
+    Expects(index < cont.size());
+    return *(cont.begin() + index);
+}
 
 } // namespace gsl
 
-
 #ifdef _MSC_VER
 
 #pragma warning(pop)
diff --git a/include/multi_span.h b/include/multi_span.h
new file mode 100644
index 0000000..a8a1af2
--- /dev/null
+++ b/include/multi_span.h
@@ -0,0 +1,2229 @@
+///////////////////////////////////////////////////////////////////////////////
+//
+// Copyright (c) 2015 Microsoft Corporation. All rights reserved.
+//
+// This code is licensed under the MIT License (MIT).
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+//
+///////////////////////////////////////////////////////////////////////////////
+
+#pragma once
+
+#ifndef GSL_MULTI_SPAN_H
+#define GSL_MULTI_SPAN_H
+
+#include "gsl_assert.h"
+#include "gsl_byte.h"
+#include "gsl_util.h"
+#include <algorithm>
+#include <array>
+#include <cassert>
+#include <cstddef>
+#include <cstdint>
+#include <functional>
+#include <iterator>
+#include <limits>
+#include <new>
+#include <numeric>
+#include <stdexcept>
+#include <type_traits>
+#include <utility>
+
+#ifdef _MSC_VER
+
+// turn off some warnings that are noisy about our Expects statements
+#pragma warning(push)
+#pragma warning(disable : 4127) // conditional expression is constant
+
+// No MSVC does constexpr fully yet
+#pragma push_macro("constexpr")
+#define constexpr
+
+// VS 2013 workarounds
+#if _MSC_VER <= 1800
+
+#define GSL_MSVC_HAS_VARIADIC_CTOR_BUG
+#define GSL_MSVC_NO_SUPPORT_FOR_MOVE_CTOR_DEFAULT
+
+// noexcept is not understood
+#ifndef GSL_THROW_ON_CONTRACT_VIOLATION
+#pragma push_macro("noexcept")
+#define noexcept /* nothing */
+#endif
+
+// turn off some misguided warnings
+#pragma warning(push)
+#pragma warning(disable : 4351) // warns about newly introduced aggregate initializer behavior
+#pragma warning(disable : 4512) // warns that assignment op could not be generated
+
+#endif // _MSC_VER <= 1800
+
+#endif // _MSC_VER
+
+#ifdef GSL_THROW_ON_CONTRACT_VIOLATION
+
+#ifdef _MSC_VER
+#pragma push_macro("noexcept")
+#endif
+
+#define noexcept /* nothing */
+
+#endif // GSL_THROW_ON_CONTRACT_VIOLATION
+
+namespace gsl
+{
+
+/*
+** begin definitions of index and bounds
+*/
+namespace details
+{
+    template <typename SizeType>
+    struct SizeTypeTraits
+    {
+        static const SizeType max_value = std::numeric_limits<SizeType>::max();
+    };
+
+    template <typename... Ts>
+    class are_integral : public std::integral_constant<bool, true>
+    {
+    };
+
+    template <typename T, typename... Ts>
+    class are_integral<T, Ts...>
+        : public std::integral_constant<bool,
+                                        std::is_integral<T>::value && are_integral<Ts...>::value>
+    {
+    };
+}
+
+template <size_t Rank>
+class index final
+{
+    static_assert(Rank > 0, "Rank must be greater than 0!");
+
+    template <size_t OtherRank>
+    friend class index;
+
+public:
+    static const size_t rank = Rank;
+    using value_type = std::ptrdiff_t;
+    using size_type = value_type;
+    using reference = std::add_lvalue_reference_t<value_type>;
+    using const_reference = std::add_lvalue_reference_t<std::add_const_t<value_type>>;
+
+    constexpr index() noexcept {}
+
+    constexpr index(const value_type (&values)[Rank]) noexcept
+    {
+        std::copy(values, values + Rank, elems);
+    }
+
+#ifdef GSL_MSVC_HAS_VARIADIC_CTOR_BUG
+    template <
+        typename T, typename... Ts,
+        typename = std::enable_if_t<((sizeof...(Ts) + 1) == Rank) && std::is_integral<T>::value &&
+                                    details::are_integral<Ts...>::value>>
+    constexpr index(T t, Ts... ds)
+        : index({narrow_cast<value_type>(t), narrow_cast<value_type>(ds)...})
+    {
+    }
+#else
+    template <typename... Ts, typename = std::enable_if_t<(sizeof...(Ts) == Rank) &&
+                                                          details::are_integral<Ts...>::value>>
+    constexpr index(Ts... ds) noexcept : elems{narrow_cast<value_type>(ds)...}
+    {
+    }
+#endif
+
+    constexpr index(const index& other) noexcept = default;
+
+    constexpr index& operator=(const index& rhs) noexcept = default;
+
+    // Preconditions: component_idx < rank
+    constexpr reference operator[](size_t component_idx)
+    {
+        Expects(component_idx < Rank); // Component index must be less than rank
+        return elems[component_idx];
+    }
+
+    // Preconditions: component_idx < rank
+    constexpr const_reference operator[](size_t component_idx) const noexcept
+    {
+        Expects(component_idx < Rank); // Component index must be less than rank
+        return elems[component_idx];
+    }
+
+    constexpr bool operator==(const index& rhs) const noexcept
+    {
+        return std::equal(elems, elems + rank, rhs.elems);
+    }
+
+    constexpr bool operator!=(const index& rhs) const noexcept { return !(this == rhs); }
+
+    constexpr index operator+() const noexcept { return *this; }
+
+    constexpr index operator-() const noexcept
+    {
+        index ret = *this;
+        std::transform(ret, ret + rank, ret, std::negate<value_type>{});
+        return ret;
+    }
+
+    constexpr index operator+(const index& rhs) const noexcept
+    {
+        index ret = *this;
+        ret += rhs;
+        return ret;
+    }
+
+    constexpr index operator-(const index& rhs) const noexcept
+    {
+        index ret = *this;
+        ret -= rhs;
+        return ret;
+    }
+
+    constexpr index& operator+=(const index& rhs) noexcept
+    {
+        std::transform(elems, elems + rank, rhs.elems, elems, std::plus<value_type>{});
+        return *this;
+    }
+
+    constexpr index& operator-=(const index& rhs) noexcept
+    {
+        std::transform(elems, elems + rank, rhs.elems, elems, std::minus<value_type>{});
+        return *this;
+    }
+
+    constexpr index operator*(value_type v) const noexcept
+    {
+        index ret = *this;
+        ret *= v;
+        return ret;
+    }
+
+    constexpr index operator/(value_type v) const noexcept
+    {
+        index ret = *this;
+        ret /= v;
+        return ret;
+    }
+
+    friend constexpr index operator*(value_type v, const index& rhs) noexcept { return rhs * v; }
+
+    constexpr index& operator*=(value_type v) noexcept
+    {
+        std::transform(elems, elems + rank, elems,
+                       [v](value_type x) { return std::multiplies<value_type>{}(x, v); });
+        return *this;
+    }
+
+    constexpr index& operator/=(value_type v) noexcept
+    {
+        std::transform(elems, elems + rank, elems,
+                       [v](value_type x) { return std::divides<value_type>{}(x, v); });
+        return *this;
+    }
+
+private:
+    value_type elems[Rank] = {};
+};
+
+#ifndef _MSC_VER
+
+struct static_bounds_dynamic_range_t
+{
+    template <typename T, typename Dummy = std::enable_if_t<std::is_integral<T>::value>>
+    constexpr operator T() const noexcept
+    {
+        return narrow_cast<T>(-1);
+    }
+
+    template <typename T, typename Dummy = std::enable_if_t<std::is_integral<T>::value>>
+    constexpr bool operator==(T other) const noexcept
+    {
+        return narrow_cast<T>(-1) == other;
+    }
+
+    template <typename T, typename Dummy = std::enable_if_t<std::is_integral<T>::value>>
+    constexpr bool operator!=(T other) const noexcept
+    {
+        return narrow_cast<T>(-1) != other;
+    }
+};
+
+template <typename T, typename Dummy = std::enable_if_t<std::is_integral<T>::value>>
+constexpr bool operator==(T left, static_bounds_dynamic_range_t right) noexcept
+{
+    return right == left;
+}
+
+template <typename T, typename Dummy = std::enable_if_t<std::is_integral<T>::value>>
+constexpr bool operator!=(T left, static_bounds_dynamic_range_t right) noexcept
+{
+    return right != left;
+}
+
+constexpr static_bounds_dynamic_range_t dynamic_range{};
+#else
+const std::ptrdiff_t dynamic_range = -1;
+#endif
+
+struct generalized_mapping_tag
+{
+};
+struct contiguous_mapping_tag : generalized_mapping_tag
+{
+};
+
+namespace details
+{
+
+    template <std::ptrdiff_t Left, std::ptrdiff_t Right>
+    struct LessThan
+    {
+        static const bool value = Left < Right;
+    };
+
+    template <std::ptrdiff_t... Ranges>
+    struct BoundsRanges
+    {
+        using size_type = std::ptrdiff_t;
+        static const size_type Depth = 0;
+        static const size_type DynamicNum = 0;
+        static const size_type CurrentRange = 1;
+        static const size_type TotalSize = 1;
+
+        // TODO : following signature is for work around VS bug
+        template <typename OtherRange>
+        BoundsRanges(const OtherRange&, bool /* firstLevel */)
+        {
+        }
+
+        BoundsRanges(const BoundsRanges&) = default;
+        BoundsRanges& operator=(const BoundsRanges&) = default;
+        BoundsRanges(const std::ptrdiff_t* const) {}
+        BoundsRanges() = default;
+
+        template <typename T, size_t Dim>
+        void serialize(T&) const
+        {
+        }
+
+        template <typename T, size_t Dim>
+        size_type linearize(const T&) const
+        {
+            return 0;
+        }
+
+        template <typename T, size_t Dim>
+        size_type contains(const T&) const
+        {
+            return -1;
+        }
+
+        size_type elementNum(size_t) const noexcept { return 0; }
+
+        size_type totalSize() const noexcept { return TotalSize; }
+
+        bool operator==(const BoundsRanges&) const noexcept { return true; }
+    };
+
+    template <std::ptrdiff_t... RestRanges>
+    struct BoundsRanges<dynamic_range, RestRanges...> : BoundsRanges<RestRanges...>
+    {
+        using Base = BoundsRanges<RestRanges...>;
+        using size_type = std::ptrdiff_t;
+        static const size_t Depth = Base::Depth + 1;
+        static const size_t DynamicNum = Base::DynamicNum + 1;
+        static const size_type CurrentRange = dynamic_range;
+        static const size_type TotalSize = dynamic_range;
+        const size_type m_bound;
+
+        BoundsRanges(const BoundsRanges&) = default;
+
+        BoundsRanges(const std::ptrdiff_t* const arr)
+            : Base(arr + 1), m_bound(*arr * this->Base::totalSize())
+        {
+            Expects(0 <= *arr);
+        }
+
+        BoundsRanges() : m_bound(0) {}
+
+        template <std::ptrdiff_t OtherRange, std::ptrdiff_t... RestOtherRanges>
+        BoundsRanges(const BoundsRanges<OtherRange, RestOtherRanges...>& other,
+                     bool /* firstLevel */ = true)
+            : Base(static_cast<const BoundsRanges<RestOtherRanges...>&>(other), false)
+            , m_bound(other.totalSize())
+        {
+        }
+
+        template <typename T, size_t Dim = 0>
+        void serialize(T& arr) const
+        {
+            arr[Dim] = elementNum();
+            this->Base::template serialize<T, Dim + 1>(arr);
+        }
+
+        template <typename T, size_t Dim = 0>
+        size_type linearize(const T& arr) const
+        {
+            const size_type index = this->Base::totalSize() * arr[Dim];
+            Expects(index < m_bound);
+            return index + this->Base::template linearize<T, Dim + 1>(arr);
+        }
+
+        template <typename T, size_t Dim = 0>
+        size_type contains(const T& arr) const
+        {
+            const ptrdiff_t last = this->Base::template contains<T, Dim + 1>(arr);
+            if (last == -1) return -1;
+            const ptrdiff_t cur = this->Base::totalSize() * arr[Dim];
+            return cur < m_bound ? cur + last : -1;
+        }
+
+        size_type totalSize() const noexcept { return m_bound; }
+
+        size_type elementNum() const noexcept { return totalSize() / this->Base::totalSize(); }
+
+        size_type elementNum(size_t dim) const noexcept
+        {
+            if (dim > 0)
+                return this->Base::elementNum(dim - 1);
+            else
+                return elementNum();
+        }
+
+        bool operator==(const BoundsRanges& rhs) const noexcept
+        {
+            return m_bound == rhs.m_bound &&
+                   static_cast<const Base&>(*this) == static_cast<const Base&>(rhs);
+        }
+    };
+
+    template <std::ptrdiff_t CurRange, std::ptrdiff_t... RestRanges>
+    struct BoundsRanges<CurRange, RestRanges...> : BoundsRanges<RestRanges...>
+    {
+        using Base = BoundsRanges<RestRanges...>;
+        using size_type = std::ptrdiff_t;
+        static const size_t Depth = Base::Depth + 1;
+        static const size_t DynamicNum = Base::DynamicNum;
+        static const size_type CurrentRange = CurRange;
+        static const size_type TotalSize =
+            Base::TotalSize == dynamic_range ? dynamic_range : CurrentRange * Base::TotalSize;
+
+        BoundsRanges(const BoundsRanges&) = default;
+
+        BoundsRanges(const std::ptrdiff_t* const arr) : Base(arr) {}
+        BoundsRanges() = default;
+
+        template <std::ptrdiff_t OtherRange, std::ptrdiff_t... RestOtherRanges>
+        BoundsRanges(const BoundsRanges<OtherRange, RestOtherRanges...>& other,
+                     bool firstLevel = true)
+            : Base(static_cast<const BoundsRanges<RestOtherRanges...>&>(other), false)
+        {
+            (void) firstLevel;
+        }
+
+        template <typename T, size_t Dim = 0>
+        void serialize(T& arr) const
+        {
+            arr[Dim] = elementNum();
+            this->Base::template serialize<T, Dim + 1>(arr);
+        }
+
+        template <typename T, size_t Dim = 0>
+        size_type linearize(const T& arr) const
+        {
+            Expects(arr[Dim] < CurrentRange); // Index is out of range
+            return this->Base::totalSize() * arr[Dim] +
+                   this->Base::template linearize<T, Dim + 1>(arr);
+        }
+
+        template <typename T, size_t Dim = 0>
+        size_type contains(const T& arr) const
+        {
+            if (arr[Dim] >= CurrentRange) return -1;
+            const size_type last = this->Base::template contains<T, Dim + 1>(arr);
+            if (last == -1) return -1;
+            return this->Base::totalSize() * arr[Dim] + last;
+        }
+
+        size_type totalSize() const noexcept { return CurrentRange * this->Base::totalSize(); }
+
+        size_type elementNum() const noexcept { return CurrentRange; }
+
+        size_type elementNum(size_t dim) const noexcept
+        {
+            if (dim > 0)
+                return this->Base::elementNum(dim - 1);
+            else
+                return elementNum();
+        }
+
+        bool operator==(const BoundsRanges& rhs) const noexcept
+        {
+            return static_cast<const Base&>(*this) == static_cast<const Base&>(rhs);
+        }
+    };
+
+    template <typename SourceType, typename TargetType>
+    struct BoundsRangeConvertible
+        : public std::integral_constant<bool, (SourceType::TotalSize >= TargetType::TotalSize ||
+                                               TargetType::TotalSize == dynamic_range ||
+                                               SourceType::TotalSize == dynamic_range ||
+                                               TargetType::TotalSize == 0)>
+    {
+    };
+
+    template <typename TypeChain>
+    struct TypeListIndexer
+    {
+        const TypeChain& obj_;
+        TypeListIndexer(const TypeChain& obj) : obj_(obj) {}
+
+        template <size_t N>
+        const TypeChain& getObj(std::true_type)
+        {
+            return obj_;
+        }
+
+        template <size_t N, typename MyChain = TypeChain, typename MyBase = typename MyChain::Base>
+        auto getObj(std::false_type)
+            -> decltype(TypeListIndexer<MyBase>(static_cast<const MyBase&>(obj_)).template get<N>())
+        {
+            return TypeListIndexer<MyBase>(static_cast<const MyBase&>(obj_)).template get<N>();
+        }
+
+        template <size_t N>
+        auto get() -> decltype(getObj<N - 1>(std::integral_constant<bool, N == 0>()))
+        {
+            return getObj<N - 1>(std::integral_constant<bool, N == 0>());
+        }
+    };
+
+    template <typename TypeChain>
+    TypeListIndexer<TypeChain> createTypeListIndexer(const TypeChain& obj)
+    {
+        return TypeListIndexer<TypeChain>(obj);
+    }
+
+    template <size_t Rank, bool Enabled = (Rank > 1),
+              typename Ret = std::enable_if_t<Enabled, index<Rank - 1>>>
+    constexpr Ret shift_left(const index<Rank>& other) noexcept
+    {
+        Ret ret{};
+        for (size_t i = 0; i < Rank - 1; ++i) {
+            ret[i] = other[i + 1];
+        }
+        return ret;
+    }
+}
+
+template <typename IndexType>
+class bounds_iterator;
+
+template <std::ptrdiff_t... Ranges>
+class static_bounds
+{
+public:
+    static_bounds(const details::BoundsRanges<Ranges...>&) {}
+};
+
+template <std::ptrdiff_t FirstRange, std::ptrdiff_t... RestRanges>
+class static_bounds<FirstRange, RestRanges...>
+{
+    using MyRanges = details::BoundsRanges<FirstRange, RestRanges...>;
+
+    MyRanges m_ranges;
+    constexpr static_bounds(const MyRanges& range) : m_ranges(range) {}
+
+    template <std::ptrdiff_t... OtherRanges>
+    friend class static_bounds;
+
+public:
+    static const size_t rank = MyRanges::Depth;
+    static const size_t dynamic_rank = MyRanges::DynamicNum;
+    static const std::ptrdiff_t static_size = MyRanges::TotalSize;
+
+    using size_type = std::ptrdiff_t;
+    using index_type = index<rank>;
+    using const_index_type = std::add_const_t<index_type>;
+    using iterator = bounds_iterator<const_index_type>;
+    using const_iterator = bounds_iterator<const_index_type>;
+    using difference_type = std::ptrdiff_t;
+    using sliced_type = static_bounds<RestRanges...>;
+    using mapping_type = contiguous_mapping_tag;
+
+    constexpr static_bounds(const static_bounds&) = default;
+
+    template <typename SourceType, typename TargetType, size_t Rank>
+    struct BoundsRangeConvertible2;
+
+    template <size_t Rank, typename SourceType, typename TargetType,
+              typename Ret = BoundsRangeConvertible2<typename SourceType::Base,
+                                                     typename TargetType::Base, Rank>>
+    static auto helpBoundsRangeConvertible(SourceType, TargetType, std::true_type) -> Ret;
+
+    template <size_t Rank, typename SourceType, typename TargetType>
+    static auto helpBoundsRangeConvertible(SourceType, TargetType, ...) -> std::false_type;
+
+    template <typename SourceType, typename TargetType, size_t Rank>
+    struct BoundsRangeConvertible2
+        : decltype(helpBoundsRangeConvertible<Rank - 1>(
+              SourceType(), TargetType(),
+              std::integral_constant<bool,
+                                     SourceType::Depth == TargetType::Depth &&
+                                         (SourceType::CurrentRange == TargetType::CurrentRange ||
+                                          TargetType::CurrentRange == dynamic_range ||
+                                          SourceType::CurrentRange == dynamic_range)>()))
+    {
+    };
+
+    template <typename SourceType, typename TargetType>
+    struct BoundsRangeConvertible2<SourceType, TargetType, 0> : std::true_type
+    {
+    };
+
+    template <typename SourceType, typename TargetType, std::ptrdiff_t Rank = TargetType::Depth>
+    struct BoundsRangeConvertible
+        : decltype(helpBoundsRangeConvertible<Rank - 1>(
+              SourceType(), TargetType(),
+              std::integral_constant<bool,
+                                     SourceType::Depth == TargetType::Depth &&
+                                         (!details::LessThan<SourceType::CurrentRange,
+                                                             TargetType::CurrentRange>::value ||
+                                          TargetType::CurrentRange == dynamic_range ||
+                                          SourceType::CurrentRange == dynamic_range)>()))
+    {
+    };
+
+    template <typename SourceType, typename TargetType>
+    struct BoundsRangeConvertible<SourceType, TargetType, 0> : std::true_type
+    {
+    };
+
+    template <std::ptrdiff_t... Ranges,
+              typename = std::enable_if_t<details::BoundsRangeConvertible<
+                  details::BoundsRanges<Ranges...>,
+                  details::BoundsRanges<FirstRange, RestRanges...>>::value>>
+    constexpr static_bounds(const static_bounds<Ranges...>& other) : m_ranges(other.m_ranges)
+    {
+        Expects((MyRanges::DynamicNum == 0 && details::BoundsRanges<Ranges...>::DynamicNum == 0) ||
+                MyRanges::DynamicNum > 0 || other.m_ranges.totalSize() >= m_ranges.totalSize());
+    }
+
+    constexpr static_bounds(std::initializer_list<size_type> il)
+        : m_ranges(static_cast<const std::ptrdiff_t*>(il.begin()))
+    {
+        // Size of the initializer list must match the rank of the array
+        Expects((MyRanges::DynamicNum == 0 && il.size() == 1 && *il.begin() == static_size) ||
+                MyRanges::DynamicNum == il.size());
+        // Size of the range must be less than the max element of the size type
+        Expects(m_ranges.totalSize() <= PTRDIFF_MAX);
+    }
+
+    constexpr static_bounds() = default;
+
+    constexpr static_bounds& operator=(const static_bounds& otherBounds)
+    {
+        new (&m_ranges) MyRanges(otherBounds.m_ranges);
+        return *this;
+    }
+
+    constexpr sliced_type slice() const noexcept
+    {
+        return sliced_type{static_cast<const details::BoundsRanges<RestRanges...>&>(m_ranges)};
+    }
+
+    constexpr size_type stride() const noexcept { return rank > 1 ? slice().size() : 1; }
+
+    constexpr size_type size() const noexcept { return m_ranges.totalSize(); }
+
+    constexpr size_type total_size() const noexcept { return m_ranges.totalSize(); }
+
+    constexpr size_type linearize(const index_type& idx) const { return m_ranges.linearize(idx); }
+
+    constexpr bool contains(const index_type& idx) const noexcept
+    {
+        return m_ranges.contains(idx) != -1;
+    }
+
+    constexpr size_type operator[](size_t index) const noexcept
+    {
+        return m_ranges.elementNum(index);
+    }
+
+    template <size_t Dim = 0>
+    constexpr size_type extent() const noexcept
+    {
+        static_assert(Dim < rank,
+                      "dimension should be less than rank (dimension count starts from 0)");
+        return details::createTypeListIndexer(m_ranges).template get<Dim>().elementNum();
+    }
+
+    template <typename IntType>
+    constexpr size_type extent(IntType dim) const noexcept
+    {
+        static_assert(std::is_integral<IntType>::value,
+                      "Dimension parameter must be supplied as an integral type.");
+        auto real_dim = narrow_cast<size_t>(dim);
+        Expects(real_dim < rank);
+
+        return m_ranges.elementNum(real_dim);
+    }
+
+    constexpr index_type index_bounds() const noexcept
+    {
+        size_type extents[rank] = {};
+        m_ranges.serialize(extents);
+        return {extents};
+    }
+
+    template <std::ptrdiff_t... Ranges>
+    constexpr bool operator==(const static_bounds<Ranges...>& rhs) const noexcept
+    {
+        return this->size() == rhs.size();
+    }
+
+    template <std::ptrdiff_t... Ranges>
+    constexpr bool operator!=(const static_bounds<Ranges...>& rhs) const noexcept
+    {
+        return !(*this == rhs);
+    }
+
+    constexpr const_iterator begin() const noexcept { return const_iterator(*this, index_type{}); }
+
+    constexpr const_iterator end() const noexcept
+    {
+        return const_iterator(*this, this->index_bounds());
+    }
+};
+
+template <size_t Rank>
+class strided_bounds
+{
+    template <size_t OtherRank>
+    friend class strided_bounds;
+
+public:
+    static const size_t rank = Rank;
+    using value_type = std::ptrdiff_t;
+    using reference = std::add_lvalue_reference_t<value_type>;
+    using const_reference = std::add_const_t<reference>;
+    using size_type = value_type;
+    using difference_type = value_type;
+    using index_type = index<rank>;
+    using const_index_type = std::add_const_t<index_type>;
+    using iterator = bounds_iterator<const_index_type>;
+    using const_iterator = bounds_iterator<const_index_type>;
+    static const value_type dynamic_rank = rank;
+    static const value_type static_size = dynamic_range;
+    using sliced_type = std::conditional_t<rank != 0, strided_bounds<rank - 1>, void>;
+    using mapping_type = generalized_mapping_tag;
+
+    constexpr strided_bounds(const strided_bounds&) noexcept = default;
+
+    constexpr strided_bounds& operator=(const strided_bounds&) noexcept = default;
+
+    constexpr strided_bounds(const value_type (&values)[rank], index_type strides)
+        : m_extents(values), m_strides(std::move(strides))
+    {
+    }
+
+    constexpr strided_bounds(const index_type& extents, const index_type& strides) noexcept
+        : m_extents(extents),
+          m_strides(strides)
+    {
+    }
+
+    constexpr index_type strides() const noexcept { return m_strides; }
+
+    constexpr size_type total_size() const noexcept
+    {
+        size_type ret = 0;
+        for (size_t i = 0; i < rank; ++i) {
+            ret += (m_extents[i] - 1) * m_strides[i];
+        }
+        return ret + 1;
+    }
+
+    constexpr size_type size() const noexcept
+    {
+        size_type ret = 1;
+        for (size_t i = 0; i < rank; ++i) {
+            ret *= m_extents[i];
+        }
+        return ret;
+    }
+
+    constexpr bool contains(const index_type& idx) const noexcept
+    {
+        for (size_t i = 0; i < rank; ++i) {
+            if (idx[i] < 0 || idx[i] >= m_extents[i]) return false;
+        }
+        return true;
+    }
+
+    constexpr size_type linearize(const index_type& idx) const noexcept
+    {
+        size_type ret = 0;
+        for (size_t i = 0; i < rank; i++) {
+            Expects(idx[i] < m_extents[i]); // index is out of bounds of the array
+            ret += idx[i] * m_strides[i];
+        }
+        return ret;
+    }
+
+    constexpr size_type stride() const noexcept { return m_strides[0]; }
+
+    template <bool Enabled = (rank > 1), typename Ret = std::enable_if_t<Enabled, sliced_type>>
+    constexpr sliced_type slice() const
+    {
+        return {details::shift_left(m_extents), details::shift_left(m_strides)};
+    }
+
+    template <size_t Dim = 0>
+    constexpr size_type extent() const noexcept
+    {
+        static_assert(Dim < Rank,
+                      "dimension should be less than rank (dimension count starts from 0)");
+        return m_extents[Dim];
+    }
+
+    constexpr index_type index_bounds() const noexcept { return m_extents; }
+    constexpr const_iterator begin() const noexcept { return const_iterator{*this, index_type{}}; }
+
+    constexpr const_iterator end() const noexcept { return const_iterator{*this, index_bounds()}; }
+
+private:
+    index_type m_extents;
+    index_type m_strides;
+};
+
+template <typename T>
+struct is_bounds : std::integral_constant<bool, false>
+{
+};
+template <std::ptrdiff_t... Ranges>
+struct is_bounds<static_bounds<Ranges...>> : std::integral_constant<bool, true>
+{
+};
+template <size_t Rank>
+struct is_bounds<strided_bounds<Rank>> : std::integral_constant<bool, true>
+{
+};
+
+template <typename IndexType>
+class bounds_iterator : public std::iterator<std::random_access_iterator_tag, IndexType>
+{
+private:
+    using Base = std::iterator<std::random_access_iterator_tag, IndexType>;
+
+public:
+    static const size_t rank = IndexType::rank;
+    using typename Base::reference;
+    using typename Base::pointer;
+    using typename Base::difference_type;
+    using typename Base::value_type;
+    using index_type = value_type;
+    using index_size_type = typename IndexType::value_type;
+    template <typename Bounds>
+    explicit bounds_iterator(const Bounds& bnd, value_type curr) noexcept
+        : boundary_(bnd.index_bounds()),
+          curr_(std::move(curr))
+    {
+        static_assert(is_bounds<Bounds>::value, "Bounds type must be provided");
+    }
+
+    constexpr reference operator*() const noexcept { return curr_; }
+
+    constexpr pointer operator->() const noexcept { return &curr_; }
+
+    constexpr bounds_iterator& operator++() noexcept
+    {
+        for (size_t i = rank; i-- > 0;) {
+            if (curr_[i] < boundary_[i] - 1) {
+                curr_[i]++;
+                return *this;
+            }
+            curr_[i] = 0;
+        }
+        // If we're here we've wrapped over - set to past-the-end.
+        curr_ = boundary_;
+        return *this;
+    }
+
+    constexpr bounds_iterator operator++(int) noexcept
+    {
+        auto ret = *this;
+        ++(*this);
+        return ret;
+    }
+
+    constexpr bounds_iterator& operator--() noexcept
+    {
+        if (!less(curr_, boundary_)) {
+            // if at the past-the-end, set to last element
+            for (size_t i = 0; i < rank; ++i) {
+                curr_[i] = boundary_[i] - 1;
+            }
+            return *this;
+        }
+        for (size_t i = rank; i-- > 0;) {
+            if (curr_[i] >= 1) {
+                curr_[i]--;
+                return *this;
+            }
+            curr_[i] = boundary_[i] - 1;
+        }
+        // If we're here the preconditions were violated
+        // "pre: there exists s such that r == ++s"
+        Expects(false);
+        return *this;
+    }
+
+    constexpr bounds_iterator operator--(int) noexcept
+    {
+        auto ret = *this;
+        --(*this);
+        return ret;
+    }
+
+    constexpr bounds_iterator operator+(difference_type n) const noexcept
+    {
+        bounds_iterator ret{*this};
+        return ret += n;
+    }
+
+    constexpr bounds_iterator& operator+=(difference_type n) noexcept
+    {
+        auto linear_idx = linearize(curr_) + n;
+        std::remove_const_t<value_type> stride = 0;
+        stride[rank - 1] = 1;
+        for (size_t i = rank - 1; i-- > 0;) {
+            stride[i] = stride[i + 1] * boundary_[i + 1];
+        }
+        for (size_t i = 0; i < rank; ++i) {
+            curr_[i] = linear_idx / stride[i];
+            linear_idx = linear_idx % stride[i];
+        }
+        // index is out of bounds of the array
+        Expects(!less(curr_, index_type{}) && !less(boundary_, curr_));
+        return *this;
+    }
+
+    constexpr bounds_iterator operator-(difference_type n) const noexcept
+    {
+        bounds_iterator ret{*this};
+        return ret -= n;
+    }
+
+    constexpr bounds_iterator& operator-=(difference_type n) noexcept { return *this += -n; }
+
+    constexpr difference_type operator-(const bounds_iterator& rhs) const noexcept
+    {
+        return linearize(curr_) - linearize(rhs.curr_);
+    }
+
+    constexpr value_type operator[](difference_type n) const noexcept { return *(*this + n); }
+
+    constexpr bool operator==(const bounds_iterator& rhs) const noexcept
+    {
+        return curr_ == rhs.curr_;
+    }
+
+    constexpr bool operator!=(const bounds_iterator& rhs) const noexcept { return !(*this == rhs); }
+
+    constexpr bool operator<(const bounds_iterator& rhs) const noexcept
+    {
+        return less(curr_, rhs.curr_);
+    }
+
+    constexpr bool operator<=(const bounds_iterator& rhs) const noexcept { return !(rhs < *this); }
+
+    constexpr bool operator>(const bounds_iterator& rhs) const noexcept { return rhs < *this; }
+
+    constexpr bool operator>=(const bounds_iterator& rhs) const noexcept { return !(rhs > *this); }
+
+    void swap(bounds_iterator& rhs) noexcept
+    {
+        std::swap(boundary_, rhs.boundary_);
+        std::swap(curr_, rhs.curr_);
+    }
+
+private:
+    constexpr bool less(index_type& one, index_type& other) const noexcept
+    {
+        for (size_t i = 0; i < rank; ++i) {
+            if (one[i] < other[i]) return true;
+        }
+        return false;
+    }
+
+    constexpr index_size_type linearize(const value_type& idx) const noexcept
+    {
+        // TODO: Smarter impl.
+        // Check if past-the-end
+        index_size_type multiplier = 1;
+        index_size_type res = 0;
+        if (!less(idx, boundary_)) {
+            res = 1;
+            for (size_t i = rank; i-- > 0;) {
+                res += (idx[i] - 1) * multiplier;
+                multiplier *= boundary_[i];
+            }
+        }
+        else
+        {
+            for (size_t i = rank; i-- > 0;) {
+                res += idx[i] * multiplier;
+                multiplier *= boundary_[i];
+            }
+        }
+        return res;
+    }
+
+    value_type boundary_;
+    std::remove_const_t<value_type> curr_;
+};
+
+template <typename IndexType>
+bounds_iterator<IndexType> operator+(typename bounds_iterator<IndexType>::difference_type n,
+                                     const bounds_iterator<IndexType>& rhs) noexcept
+{
+    return rhs + n;
+}
+
+namespace details
+{
+    template <typename Bounds>
+    constexpr std::enable_if_t<
+        std::is_same<typename Bounds::mapping_type, generalized_mapping_tag>::value,
+        typename Bounds::index_type>
+    make_stride(const Bounds& bnd) noexcept
+    {
+        return bnd.strides();
+    }
+
+    // Make a stride vector from bounds, assuming contiguous memory.
+    template <typename Bounds>
+    constexpr std::enable_if_t<
+        std::is_same<typename Bounds::mapping_type, contiguous_mapping_tag>::value,
+        typename Bounds::index_type>
+    make_stride(const Bounds& bnd) noexcept
+    {
+        auto extents = bnd.index_bounds();
+        typename Bounds::size_type stride[Bounds::rank] = {};
+
+        stride[Bounds::rank - 1] = 1;
+        for (size_t i = 1; i < Bounds::rank; ++i) {
+            stride[Bounds::rank - i - 1] = stride[Bounds::rank - i] * extents[Bounds::rank - i];
+        }
+        return {stride};
+    }
+
+    template <typename BoundsSrc, typename BoundsDest>
+    void verifyBoundsReshape(const BoundsSrc& src, const BoundsDest& dest)
+    {
+        static_assert(is_bounds<BoundsSrc>::value && is_bounds<BoundsDest>::value,
+                      "The src type and dest type must be bounds");
+        static_assert(std::is_same<typename BoundsSrc::mapping_type, contiguous_mapping_tag>::value,
+                      "The source type must be a contiguous bounds");
+        static_assert(BoundsDest::static_size == dynamic_range ||
+                          BoundsSrc::static_size == dynamic_range ||
+                          BoundsDest::static_size == BoundsSrc::static_size,
+                      "The source bounds must have same size as dest bounds");
+        Expects(src.size() == dest.size());
+    }
+
+} // namespace details
+
+template <typename Span>
+class contiguous_span_iterator;
+template <typename Span>
+class general_span_iterator;
+
+template <std::ptrdiff_t DimSize = dynamic_range>
+struct dim
+{
+    static const std::ptrdiff_t value = DimSize;
+};
+template <>
+struct dim<dynamic_range>
+{
+    static const std::ptrdiff_t value = dynamic_range;
+    const std::ptrdiff_t dvalue;
+    dim(std::ptrdiff_t size) : dvalue(size) {}
+};
+
+template <typename ValueType, std::ptrdiff_t FirstDimension = dynamic_range,
+          std::ptrdiff_t... RestDimensions>
+class multi_span;
+
+template <typename ValueType, size_t Rank>
+class strided_span;
+
+namespace details
+{
+    template <typename T, typename = std::true_type>
+    struct SpanTypeTraits
+    {
+        using value_type = T;
+        using size_type = size_t;
+    };
+
+    template <typename Traits>
+    struct SpanTypeTraits<Traits, typename std::is_reference<typename Traits::span_traits&>::type>
+    {
+        using value_type = typename Traits::span_traits::value_type;
+        using size_type = typename Traits::span_traits::size_type;
+    };
+
+    template <typename T, std::ptrdiff_t... Ranks>
+    struct SpanArrayTraits
+    {
+        using type = multi_span<T, Ranks...>;
+        using value_type = T;
+        using bounds_type = static_bounds<Ranks...>;
+        using pointer = T*;
+        using reference = T&;
+    };
+    template <typename T, std::ptrdiff_t N, std::ptrdiff_t... Ranks>
+    struct SpanArrayTraits<T[N], Ranks...> : SpanArrayTraits<T, Ranks..., N>
+    {
+    };
+
+    template <typename BoundsType>
+    BoundsType newBoundsHelperImpl(std::ptrdiff_t totalSize, std::true_type) // dynamic size
+    {
+        Expects(totalSize >= 0 && totalSize <= PTRDIFF_MAX);
+        return BoundsType{totalSize};
+    }
+    template <typename BoundsType>
+    BoundsType newBoundsHelperImpl(std::ptrdiff_t totalSize, std::false_type) // static size
+    {
+        Expects(BoundsType::static_size <= totalSize);
+        return {};
+    }
+    template <typename BoundsType>
+    BoundsType newBoundsHelper(std::ptrdiff_t totalSize)
+    {
+        static_assert(BoundsType::dynamic_rank <= 1, "dynamic rank must less or equal to 1");
+        return newBoundsHelperImpl<BoundsType>(
+            totalSize, std::integral_constant<bool, BoundsType::dynamic_rank == 1>());
+    }
+
+    struct Sep
+    {
+    };
+
+    template <typename T, typename... Args>
+    T static_as_multi_span_helper(Sep, Args... args)
+    {
+        return T{narrow_cast<typename T::size_type>(args)...};
+    }
+    template <typename T, typename Arg, typename... Args>
+    std::enable_if_t<
+        !std::is_same<Arg, dim<dynamic_range>>::value && !std::is_same<Arg, Sep>::value, T>
+        static_as_multi_span_helper(Arg, Args... args)
+    {
+        return static_as_multi_span_helper<T>(args...);
+    }
+    template <typename T, typename... Args>
+    T static_as_multi_span_helper(dim<dynamic_range> val, Args... args)
+    {
+        return static_as_multi_span_helper<T>(args..., val.dvalue);
+    }
+
+    template <typename... Dimensions>
+    struct static_as_multi_span_static_bounds_helper
+    {
+        using type = static_bounds<(Dimensions::value)...>;
+    };
+
+    template <typename T>
+    struct is_multi_span_oracle : std::false_type
+    {
+    };
+
+    template <typename ValueType, std::ptrdiff_t FirstDimension, std::ptrdiff_t... RestDimensions>
+    struct is_multi_span_oracle<multi_span<ValueType, FirstDimension, RestDimensions...>>
+        : std::true_type
+    {
+    };
+
+    template <typename ValueType, std::ptrdiff_t Rank>
+    struct is_multi_span_oracle<strided_span<ValueType, Rank>> : std::true_type
+    {
+    };
+
+    template <typename T>
+    struct is_multi_span : is_multi_span_oracle<std::remove_cv_t<T>>
+    {
+    };
+}
+
+template <typename ValueType, std::ptrdiff_t FirstDimension, std::ptrdiff_t... RestDimensions>
+class multi_span
+{
+    // TODO do we still need this?
+    template <typename ValueType2, std::ptrdiff_t FirstDimension2,
+              std::ptrdiff_t... RestDimensions2>
+    friend class multi_span;
+
+public:
+    using bounds_type = static_bounds<FirstDimension, RestDimensions...>;
+    static const size_t Rank = bounds_type::rank;
+    using size_type = typename bounds_type::size_type;
+    using index_type = typename bounds_type::index_type;
+    using value_type = ValueType;
+    using const_value_type = std::add_const_t<value_type>;
+    using pointer = std::add_pointer_t<value_type>;
+    using reference = std::add_lvalue_reference_t<value_type>;
+    using iterator = contiguous_span_iterator<multi_span>;
+    using const_span = multi_span<const_value_type, FirstDimension, RestDimensions...>;
+    using const_iterator = contiguous_span_iterator<const_span>;
+    using reverse_iterator = std::reverse_iterator<iterator>;
+    using const_reverse_iterator = std::reverse_iterator<const_iterator>;
+    using sliced_type =
+        std::conditional_t<Rank == 1, value_type, multi_span<value_type, RestDimensions...>>;
+
+private:
+    pointer data_;
+    bounds_type bounds_;
+
+    friend iterator;
+    friend const_iterator;
+
+public:
+    // default constructor - same as constructing from nullptr_t
+    constexpr multi_span() noexcept : multi_span(nullptr, bounds_type{})
+    {
+        static_assert(bounds_type::dynamic_rank != 0 ||
+                          (bounds_type::dynamic_rank == 0 && bounds_type::static_size == 0),
+                      "Default construction of multi_span<T> only possible "
+                      "for dynamic or fixed, zero-length spans.");
+    }
+
+    // construct from nullptr - get an empty multi_span
+    constexpr multi_span(std::nullptr_t) noexcept : multi_span(nullptr, bounds_type{})
+    {
+        static_assert(bounds_type::dynamic_rank != 0 ||
+                          (bounds_type::dynamic_rank == 0 && bounds_type::static_size == 0),
+                      "nullptr_t construction of multi_span<T> only possible "
+                      "for dynamic or fixed, zero-length spans.");
+    }
+
+    // construct from nullptr with size of 0 (helps with template function calls)
+    template <class IntType, typename = std::enable_if_t<std::is_integral<IntType>::value>>
+    constexpr multi_span(std::nullptr_t, IntType size) noexcept : multi_span(nullptr, bounds_type{})
+    {
+        static_assert(bounds_type::dynamic_rank != 0 ||
+                          (bounds_type::dynamic_rank == 0 && bounds_type::static_size == 0),
+                      "nullptr_t construction of multi_span<T> only possible "
+                      "for dynamic or fixed, zero-length spans.");
+        Expects(size == 0);
+    }
+
+    // construct from a single element
+    constexpr multi_span(reference data) noexcept : multi_span(&data, bounds_type{1})
+    {
+        static_assert(bounds_type::dynamic_rank > 0 || bounds_type::static_size == 0 ||
+                          bounds_type::static_size == 1,
+                      "Construction from a single element only possible "
+                      "for dynamic or fixed spans of length 0 or 1.");
+    }
+
+    // prevent constructing from temporaries for single-elements
+    constexpr multi_span(value_type&&) = delete;
+
+    // construct from pointer + length
+    constexpr multi_span(pointer ptr, size_type size) noexcept : multi_span(ptr, bounds_type{size})
+    {
+    }
+
+    // construct from pointer + length - multidimensional
+    constexpr multi_span(pointer data, bounds_type bounds) noexcept : data_(data),
+                                                                      bounds_(std::move(bounds))
+    {
+        Expects((bounds_.size() > 0 && data != nullptr) || bounds_.size() == 0);
+    }
+
+    // construct from begin,end pointer pair
+    template <typename Ptr,
+              typename = std::enable_if_t<std::is_convertible<Ptr, pointer>::value &&
+                                          details::LessThan<bounds_type::dynamic_rank, 2>::value>>
+    constexpr multi_span(pointer begin, Ptr end)
+        : multi_span(begin,
+                     details::newBoundsHelper<bounds_type>(static_cast<pointer>(end) - begin))
+    {
+        Expects(begin != nullptr && end != nullptr && begin <= static_cast<pointer>(end));
+    }
+
+    // construct from n-dimensions static array
+    template <typename T, size_t N, typename Helper = details::SpanArrayTraits<T, N>>
+    constexpr multi_span(T (&arr)[N])
+        : multi_span(reinterpret_cast<pointer>(arr), bounds_type{typename Helper::bounds_type{}})
+    {
+        static_assert(std::is_convertible<typename Helper::value_type(*)[], value_type(*)[]>::value,
+                      "Cannot convert from source type to target multi_span type.");
+        static_assert(std::is_convertible<typename Helper::bounds_type, bounds_type>::value,
+                      "Cannot construct a multi_span from an array with fewer elements.");
+    }
+
+    // construct from n-dimensions dynamic array (e.g. new int[m][4])
+    // (precedence will be lower than the 1-dimension pointer)
+    template <typename T, typename Helper = details::SpanArrayTraits<T, dynamic_range>>
+    constexpr multi_span(T* const& data, size_type size)
+        : multi_span(reinterpret_cast<pointer>(data), typename Helper::bounds_type{size})
+    {
+        static_assert(std::is_convertible<typename Helper::value_type(*)[], value_type(*)[]>::value,
+                      "Cannot convert from source type to target multi_span type.");
+    }
+
+    // construct from std::array
+    template <typename T, size_t N>
+    constexpr multi_span(std::array<T, N>& arr)
+        : multi_span(arr.data(), bounds_type{static_bounds<N>{}})
+    {
+        static_assert(
+            std::is_convertible<T(*)[], typename std::remove_const_t<value_type>(*)[]>::value,
+            "Cannot convert from source type to target multi_span type.");
+        static_assert(std::is_convertible<static_bounds<N>, bounds_type>::value,
+                      "You cannot construct a multi_span from a std::array of smaller size.");
+    }
+
+    // construct from const std::array
+    template <typename T, size_t N>
+    constexpr multi_span(const std::array<std::remove_const_t<value_type>, N>& arr)
+        : multi_span(arr.data(), static_bounds<N>())
+    {
+        static_assert(std::is_convertible<T(*)[], std::remove_const_t<value_type>>::value,
+                      "Cannot convert from source type to target multi_span type.");
+        static_assert(std::is_convertible<static_bounds<N>, bounds_type>::value,
+                      "You cannot construct a multi_span from a std::array of smaller size.");
+    }
+
+    // prevent constructing from temporary std::array
+    template <typename T, size_t N>
+    constexpr multi_span(std::array<T, N>&& arr) = delete;
+
+    // construct from containers
+    // future: could use contiguous_iterator_traits to identify only contiguous containers
+    // type-requirements: container must have .size(), operator[] which are value_type compatible
+    template <typename Cont, typename DataType = typename Cont::value_type,
+              typename = std::enable_if_t<
+                  !details::is_multi_span<Cont>::value &&
+                  std::is_convertible<DataType (*)[], value_type (*)[]>::value &&
+                  std::is_same<std::decay_t<decltype(std::declval<Cont>().size(),
+                                                     *std::declval<Cont>().data())>,
+                               DataType>::value>>
+    constexpr multi_span(Cont& cont)
+        : multi_span(static_cast<pointer>(cont.data()),
+                     details::newBoundsHelper<bounds_type>(narrow_cast<size_type>(cont.size())))
+    {
+    }
+
+    // prevent constructing from temporary containers
+    template <typename Cont, typename DataType = typename Cont::value_type,
+              typename = std::enable_if_t<
+                  !details::is_multi_span<Cont>::value &&
+                  std::is_convertible<DataType (*)[], value_type (*)[]>::value &&
+                  std::is_same<std::decay_t<decltype(std::declval<Cont>().size(),
+                                                     *std::declval<Cont>().data())>,
+                               DataType>::value>>
+    explicit constexpr multi_span(Cont&& cont) = delete;
+
+    // construct from a convertible multi_span
+    template <typename OtherValueType, std::ptrdiff_t... OtherDimensions,
+              typename OtherBounds = static_bounds<OtherDimensions...>,
+              typename = std::enable_if_t<std::is_convertible<OtherValueType, ValueType>::value &&
+                                          std::is_convertible<OtherBounds, bounds_type>::value>>
+    constexpr multi_span(multi_span<OtherValueType, OtherDimensions...> other) noexcept
+        : data_(other.data_),
+          bounds_(other.bounds_)
+    {
+    }
+
+// trivial copy and move
+#ifndef GSL_MSVC_NO_SUPPORT_FOR_MOVE_CTOR_DEFAULT
+    constexpr multi_span(multi_span&&) = default;
+#endif
+    constexpr multi_span(const multi_span&) = default;
+
+// trivial assignment
+#ifndef GSL_MSVC_NO_SUPPORT_FOR_MOVE_CTOR_DEFAULT
+    constexpr multi_span& operator=(multi_span&&) = default;
+#endif
+    constexpr multi_span& operator=(const multi_span&) = default;
+
+    // first() - extract the first Count elements into a new multi_span
+    template <std::ptrdiff_t Count>
+    constexpr multi_span<ValueType, Count> first() const noexcept
+    {
+        static_assert(Count >= 0, "Count must be >= 0.");
+        static_assert(bounds_type::static_size == dynamic_range ||
+                          Count <= bounds_type::static_size,
+                      "Count is out of bounds.");
+
+        Expects(bounds_type::static_size != dynamic_range || Count <= this->size());
+        return {this->data(), Count};
+    }
+
+    // first() - extract the first count elements into a new multi_span
+    constexpr multi_span<ValueType, dynamic_range> first(size_type count) const noexcept
+    {
+        Expects(count >= 0 && count <= this->size());
+        return {this->data(), count};
+    }
+
+    // last() - extract the last Count elements into a new multi_span
+    template <std::ptrdiff_t Count>
+    constexpr multi_span<ValueType, Count> last() const noexcept
+    {
+        static_assert(Count >= 0, "Count must be >= 0.");
+        static_assert(bounds_type::static_size == dynamic_range ||
+                          Count <= bounds_type::static_size,
+                      "Count is out of bounds.");
+
+        Expects(bounds_type::static_size != dynamic_range || Count <= this->size());
+        return {this->data() + this->size() - Count, Count};
+    }
+
+    // last() - extract the last count elements into a new multi_span
+    constexpr multi_span<ValueType, dynamic_range> last(size_type count) const noexcept
+    {
+        Expects(count >= 0 && count <= this->size());
+        return {this->data() + this->size() - count, count};
+    }
+
+    // subspan() - create a subview of Count elements starting at Offset
+    template <std::ptrdiff_t Offset, std::ptrdiff_t Count>
+    constexpr multi_span<ValueType, Count> subspan() const noexcept
+    {
+        static_assert(Count >= 0, "Count must be >= 0.");
+        static_assert(Offset >= 0, "Offset must be >= 0.");
+        static_assert(bounds_type::static_size == dynamic_range ||
+                          ((Offset <= bounds_type::static_size) &&
+                           Count <= bounds_type::static_size - Offset),
+                      "You must describe a sub-range within bounds of the multi_span.");
+
+        Expects(bounds_type::static_size != dynamic_range ||
+                (Offset <= this->size() && Count <= this->size() - Offset));
+        return {this->data() + Offset, Count};
+    }
+
+    // subspan() - create a subview of count elements starting at offset
+    // supplying dynamic_range for count will consume all available elements from offset
+    constexpr multi_span<ValueType, dynamic_range> subspan(size_type offset,
+                                                           size_type count = dynamic_range) const
+        noexcept
+    {
+        Expects((offset >= 0 && offset <= this->size()) &&
+                (count == dynamic_range || (count <= this->size() - offset)));
+        return {this->data() + offset, count == dynamic_range ? this->length() - offset : count};
+    }
+
+    // section - creates a non-contiguous, strided multi_span from a contiguous one
+    constexpr strided_span<ValueType, Rank> section(index_type origin, index_type extents) const
+        noexcept
+    {
+        size_type size = this->bounds().total_size() - this->bounds().linearize(origin);
+        return {&this->operator[](origin), size,
+                strided_bounds<Rank>{extents, details::make_stride(bounds())}};
+    }
+
+    // length of the multi_span in elements
+    constexpr size_type size() const noexcept { return bounds_.size(); }
+
+    // length of the multi_span in elements
+    constexpr size_type length() const noexcept { return this->size(); }
+
+    // length of the multi_span in bytes
+    constexpr size_type size_bytes() const noexcept { return sizeof(value_type) * this->size(); }
+
+    // length of the multi_span in bytes
+    constexpr size_type length_bytes() const noexcept { return this->size_bytes(); }
+
+    constexpr bool empty() const noexcept { return this->size() == 0; }
+
+    static constexpr std::size_t rank() { return Rank; }
+
+    template <size_t Dim = 0>
+    constexpr size_type extent() const noexcept
+    {
+        static_assert(Dim < Rank,
+                      "Dimension should be less than rank (dimension count starts from 0).");
+        return bounds_.template extent<Dim>();
+    }
+
+    template <typename IntType>
+    constexpr size_type extent(IntType dim) const noexcept
+    {
+        return bounds_.extent(dim);
+    }
+
+    constexpr bounds_type bounds() const noexcept { return bounds_; }
+
+    constexpr pointer data() const noexcept { return data_; }
+
+    template <typename FirstIndex>
+    constexpr reference operator()(FirstIndex index)
+    {
+        return this->operator[](narrow_cast<std::ptrdiff_t>(index));
+    }
+
+    template <typename FirstIndex, typename... OtherIndices>
+    constexpr reference operator()(FirstIndex index, OtherIndices... indices)
+    {
+        index_type idx = {narrow_cast<std::ptrdiff_t>(index),
+                          narrow_cast<std::ptrdiff_t>(indices...)};
+        return this->operator[](idx);
+    }
+
+    constexpr reference operator[](const index_type& idx) const noexcept
+    {
+        return data_[bounds_.linearize(idx)];
+    }
+
+    template <bool Enabled = (Rank > 1), typename Ret = std::enable_if_t<Enabled, sliced_type>>
+    constexpr Ret operator[](size_type idx) const noexcept
+    {
+        Expects(idx < bounds_.size()); // index is out of bounds of the array
+        const size_type ridx = idx * bounds_.stride();
+
+        // index is out of bounds of the underlying data
+        Expects(ridx < bounds_.total_size());
+        return Ret{data_ + ridx, bounds_.slice()};
+    }
+
+    constexpr iterator begin() const noexcept { return iterator{this, true}; }
+
+    constexpr iterator end() const noexcept { return iterator{this, false}; }
+
+    constexpr const_iterator cbegin() const noexcept
+    {
+        return const_iterator{reinterpret_cast<const const_span*>(this), true};
+    }
+
+    constexpr const_iterator cend() const noexcept
+    {
+        return const_iterator{reinterpret_cast<const const_span*>(this), false};
+    }
+
+    constexpr reverse_iterator rbegin() const noexcept { return reverse_iterator{end()}; }
+
+    constexpr reverse_iterator rend() const noexcept { return reverse_iterator{begin()}; }
+
+    constexpr const_reverse_iterator crbegin() const noexcept
+    {
+        return const_reverse_iterator{cend()};
+    }
+
+    constexpr const_reverse_iterator crend() const noexcept
+    {
+        return const_reverse_iterator{cbegin()};
+    }
+
+    template <typename OtherValueType, std::ptrdiff_t... OtherDimensions,
+              typename Dummy = std::enable_if_t<std::is_same<
+                  std::remove_cv_t<value_type>, std::remove_cv_t<OtherValueType>>::value>>
+    constexpr bool operator==(const multi_span<OtherValueType, OtherDimensions...>& other) const
+        noexcept
+    {
+        return bounds_.size() == other.bounds_.size() &&
+               (data_ == other.data_ || std::equal(this->begin(), this->end(), other.begin()));
+    }
+
+    template <typename OtherValueType, std::ptrdiff_t... OtherDimensions,
+              typename Dummy = std::enable_if_t<std::is_same<
+                  std::remove_cv_t<value_type>, std::remove_cv_t<OtherValueType>>::value>>
+    constexpr bool operator!=(const multi_span<OtherValueType, OtherDimensions...>& other) const
+        noexcept
+    {
+        return !(*this == other);
+    }
+
+    template <typename OtherValueType, std::ptrdiff_t... OtherDimensions,
+              typename Dummy = std::enable_if_t<std::is_same<
+                  std::remove_cv_t<value_type>, std::remove_cv_t<OtherValueType>>::value>>
+    constexpr bool operator<(const multi_span<OtherValueType, OtherDimensions...>& other) const
+        noexcept
+    {
+        return std::lexicographical_compare(this->begin(), this->end(), other.begin(), other.end());
+    }
+
+    template <typename OtherValueType, std::ptrdiff_t... OtherDimensions,
+              typename Dummy = std::enable_if_t<std::is_same<
+                  std::remove_cv_t<value_type>, std::remove_cv_t<OtherValueType>>::value>>
+    constexpr bool operator<=(const multi_span<OtherValueType, OtherDimensions...>& other) const
+        noexcept
+    {
+        return !(other < *this);
+    }
+
+    template <typename OtherValueType, std::ptrdiff_t... OtherDimensions,
+              typename Dummy = std::enable_if_t<std::is_same<
+                  std::remove_cv_t<value_type>, std::remove_cv_t<OtherValueType>>::value>>
+    constexpr bool operator>(const multi_span<OtherValueType, OtherDimensions...>& other) const
+        noexcept
+    {
+        return (other < *this);
+    }
+
+    template <typename OtherValueType, std::ptrdiff_t... OtherDimensions,
+              typename Dummy = std::enable_if_t<std::is_same<
+                  std::remove_cv_t<value_type>, std::remove_cv_t<OtherValueType>>::value>>
+    constexpr bool operator>=(const multi_span<OtherValueType, OtherDimensions...>& other) const
+        noexcept
+    {
+        return !(*this < other);
+    }
+};
+
+//
+// Free functions for manipulating spans
+//
+
+// reshape a multi_span into a different dimensionality
+// DimCount and Enabled here are workarounds for a bug in MSVC 2015
+template <typename SpanType, typename... Dimensions2, size_t DimCount = sizeof...(Dimensions2),
+          bool Enabled = (DimCount > 0), typename = std::enable_if_t<Enabled>>
+constexpr auto as_multi_span(SpanType s, Dimensions2... dims)
+    -> multi_span<typename SpanType::value_type, Dimensions2::value...>
+{
+    static_assert(details::is_multi_span<SpanType>::value,
+                  "Variadic as_multi_span() is for reshaping existing spans.");
+    using BoundsType =
+        typename multi_span<typename SpanType::value_type, (Dimensions2::value)...>::bounds_type;
+    auto tobounds = details::static_as_multi_span_helper<BoundsType>(dims..., details::Sep{});
+    details::verifyBoundsReshape(s.bounds(), tobounds);
+    return {s.data(), tobounds};
+}
+
+// convert a multi_span<T> to a multi_span<const byte>
+template <typename U, std::ptrdiff_t... Dimensions>
+multi_span<const byte, dynamic_range> as_bytes(multi_span<U, Dimensions...> s) noexcept
+{
+    static_assert(std::is_trivial<std::decay_t<U>>::value,
+                  "The value_type of multi_span must be a trivial type.");
+    return {reinterpret_cast<const byte*>(s.data()), s.size_bytes()};
+}
+
+// convert a multi_span<T> to a multi_span<byte> (a writeable byte multi_span)
+// this is not currently a portable function that can be relied upon to work
+// on all implementations. It should be considered an experimental extension
+// to the standard GSL interface.
+template <typename U, std::ptrdiff_t... Dimensions>
+multi_span<byte> as_writeable_bytes(multi_span<U, Dimensions...> s) noexcept
+{
+    static_assert(std::is_trivial<std::decay_t<U>>::value,
+                  "The value_type of multi_span must be a trivial type.");
+    return {reinterpret_cast<byte*>(s.data()), s.size_bytes()};
+}
+
+// convert a multi_span<const byte> to a multi_span<const T>
+// this is not currently a portable function that can be relied upon to work
+// on all implementations. It should be considered an experimental extension
+// to the standard GSL interface.
+template <typename U, std::ptrdiff_t... Dimensions>
+constexpr auto as_multi_span(multi_span<const byte, Dimensions...> s) noexcept -> multi_span<
+    const U, static_cast<std::ptrdiff_t>(
+                 multi_span<const byte, Dimensions...>::bounds_type::static_size != dynamic_range
+                     ? (static_cast<size_t>(
+                            multi_span<const byte, Dimensions...>::bounds_type::static_size) /
+                        sizeof(U))
+                     : dynamic_range)>
+{
+    using ConstByteSpan = multi_span<const byte, Dimensions...>;
+    static_assert(
+        std::is_trivial<std::decay_t<U>>::value &&
+            (ConstByteSpan::bounds_type::static_size == dynamic_range ||
+             ConstByteSpan::bounds_type::static_size % narrow_cast<std::ptrdiff_t>(sizeof(U)) == 0),
+        "Target type must be a trivial type and its size must match the byte array size");
+
+    Expects((s.size_bytes() % sizeof(U)) == 0 && (s.size_bytes() / sizeof(U)) < PTRDIFF_MAX);
+    return {reinterpret_cast<const U*>(s.data()),
+            s.size_bytes() / narrow_cast<std::ptrdiff_t>(sizeof(U))};
+}
+
+// convert a multi_span<byte> to a multi_span<T>
+// this is not currently a portable function that can be relied upon to work
+// on all implementations. It should be considered an experimental extension
+// to the standard GSL interface.
+template <typename U, std::ptrdiff_t... Dimensions>
+constexpr auto as_multi_span(multi_span<byte, Dimensions...> s) noexcept
+    -> multi_span<U, narrow_cast<std::ptrdiff_t>(
+                         multi_span<byte, Dimensions...>::bounds_type::static_size != dynamic_range
+                             ? static_cast<std::size_t>(
+                                   multi_span<byte, Dimensions...>::bounds_type::static_size) /
+                                   sizeof(U)
+                             : dynamic_range)>
+{
+    using ByteSpan = multi_span<byte, Dimensions...>;
+    static_assert(
+        std::is_trivial<std::decay_t<U>>::value &&
+            (ByteSpan::bounds_type::static_size == dynamic_range ||
+             ByteSpan::bounds_type::static_size % static_cast<std::size_t>(sizeof(U)) == 0),
+        "Target type must be a trivial type and its size must match the byte array size");
+
+    Expects((s.size_bytes() % sizeof(U)) == 0);
+    return {reinterpret_cast<U*>(s.data()),
+            s.size_bytes() / narrow_cast<std::ptrdiff_t>(sizeof(U))};
+}
+
+template <typename T, std::ptrdiff_t... Dimensions>
+constexpr auto as_multi_span(T* const& ptr, dim<Dimensions>... args)
+    -> multi_span<std::remove_all_extents_t<T>, Dimensions...>
+{
+    return {reinterpret_cast<std::remove_all_extents_t<T>*>(ptr),
+            details::static_as_multi_span_helper<static_bounds<Dimensions...>>(args...,
+                                                                               details::Sep{})};
+}
+
+template <typename T>
+constexpr auto as_multi_span(T* arr, std::ptrdiff_t len) ->
+    typename details::SpanArrayTraits<T, dynamic_range>::type
+{
+    return {reinterpret_cast<std::remove_all_extents_t<T>*>(arr), len};
+}
+
+template <typename T, size_t N>
+constexpr auto as_multi_span(T (&arr)[N]) -> typename details::SpanArrayTraits<T, N>::type
+{
+    return {arr};
+}
+
+template <typename T, size_t N>
+constexpr multi_span<const T, N> as_multi_span(const std::array<T, N>& arr)
+{
+    return {arr};
+}
+
+template <typename T, size_t N>
+constexpr multi_span<const T, N> as_multi_span(const std::array<T, N>&&) = delete;
+
+template <typename T, size_t N>
+constexpr multi_span<T, N> as_multi_span(std::array<T, N>& arr)
+{
+    return {arr};
+}
+
+template <typename T>
+constexpr multi_span<T, dynamic_range> as_multi_span(T* begin, T* end)
+{
+    return {begin, end};
+}
+
+template <typename Cont>
+constexpr auto as_multi_span(Cont& arr) -> std::enable_if_t<
+    !details::is_multi_span<std::decay_t<Cont>>::value,
+    multi_span<std::remove_reference_t<decltype(arr.size(), *arr.data())>, dynamic_range>>
+{
+    Expects(arr.size() < PTRDIFF_MAX);
+    return {arr.data(), narrow_cast<std::ptrdiff_t>(arr.size())};
+}
+
+template <typename Cont>
+constexpr auto as_multi_span(Cont&& arr) -> std::enable_if_t<
+    !details::is_multi_span<std::decay_t<Cont>>::value,
+    multi_span<std::remove_reference_t<decltype(arr.size(), *arr.data())>, dynamic_range>> = delete;
+
+// from basic_string which doesn't have nonconst .data() member like other contiguous containers
+template <typename CharT, typename Traits, typename Allocator>
+constexpr auto as_multi_span(std::basic_string<CharT, Traits, Allocator>& str)
+    -> multi_span<CharT, dynamic_range>
+{
+    Expects(str.size() < PTRDIFF_MAX);
+    return {&str[0], narrow_cast<std::ptrdiff_t>(str.size())};
+}
+
+// strided_span is an extension that is not strictly part of the GSL at this time.
+// It is kept here while the multidimensional interface is still being defined.
+template <typename ValueType, size_t Rank>
+class strided_span
+{
+public:
+    using bounds_type = strided_bounds<Rank>;
+    using size_type = typename bounds_type::size_type;
+    using index_type = typename bounds_type::index_type;
+    using value_type = ValueType;
+    using const_value_type = std::add_const_t<value_type>;
+    using pointer = std::add_pointer_t<value_type>;
+    using reference = std::add_lvalue_reference_t<value_type>;
+    using iterator = general_span_iterator<strided_span>;
+    using const_strided_span = strided_span<const_value_type, Rank>;
+    using const_iterator = general_span_iterator<const_strided_span>;
+    using reverse_iterator = std::reverse_iterator<iterator>;
+    using const_reverse_iterator = std::reverse_iterator<const_iterator>;
+    using sliced_type =
+        std::conditional_t<Rank == 1, value_type, strided_span<value_type, Rank - 1>>;
+
+private:
+    pointer data_;
+    bounds_type bounds_;
+
+    friend iterator;
+    friend const_iterator;
+    template <typename OtherValueType, size_t OtherRank>
+    friend class strided_span;
+
+public:
+    // from raw data
+    constexpr strided_span(pointer ptr, size_type size, bounds_type bounds)
+        : data_(ptr), bounds_(std::move(bounds))
+    {
+        Expects((bounds_.size() > 0 && ptr != nullptr) || bounds_.size() == 0);
+        // Bounds cross data boundaries
+        Expects(this->bounds().total_size() <= size);
+        (void) size;
+    }
+
+    // from static array of size N
+    template <size_type N>
+    constexpr strided_span(value_type (&values)[N], bounds_type bounds)
+        : strided_span(values, N, std::move(bounds))
+    {
+    }
+
+    // from array view
+    template <typename OtherValueType, std::ptrdiff_t... Dimensions,
+              bool Enabled1 = (sizeof...(Dimensions) == Rank),
+              bool Enabled2 = std::is_convertible<OtherValueType*, ValueType*>::value,
+              typename Dummy = std::enable_if_t<Enabled1 && Enabled2>>
+    constexpr strided_span(multi_span<OtherValueType, Dimensions...> av, bounds_type bounds)
+        : strided_span(av.data(), av.bounds().total_size(), std::move(bounds))
+    {
+    }
+
+    // convertible
+    template <typename OtherValueType, typename Dummy = std::enable_if_t<std::is_convertible<
+                                           OtherValueType (*)[], value_type (*)[]>::value>>
+    constexpr strided_span(const strided_span<OtherValueType, Rank>& other)
+        : data_(other.data_), bounds_(other.bounds_)
+    {
+    }
+
+    // convert from bytes
+    template <typename OtherValueType>
+    constexpr strided_span<
+        typename std::enable_if<std::is_same<value_type, const byte>::value, OtherValueType>::type,
+        Rank>
+    as_strided_span() const
+    {
+        static_assert((sizeof(OtherValueType) >= sizeof(value_type)) &&
+                          (sizeof(OtherValueType) % sizeof(value_type) == 0),
+                      "OtherValueType should have a size to contain a multiple of ValueTypes");
+        auto d = narrow_cast<size_type>(sizeof(OtherValueType) / sizeof(value_type));
+
+        size_type size = this->bounds().total_size() / d;
+        return {const_cast<OtherValueType*>(reinterpret_cast<const OtherValueType*>(this->data())),
+                size, bounds_type{resize_extent(this->bounds().index_bounds(), d),
+                                  resize_stride(this->bounds().strides(), d)}};
+    }
+
+    constexpr strided_span section(index_type origin, index_type extents) const
+    {
+        size_type size = this->bounds().total_size() - this->bounds().linearize(origin);
+        return {&this->operator[](origin), size,
+                bounds_type{extents, details::make_stride(bounds())}};
+    }
+
+    constexpr reference operator[](const index_type& idx) const
+    {
+        return data_[bounds_.linearize(idx)];
+    }
+
+    template <bool Enabled = (Rank > 1), typename Ret = std::enable_if_t<Enabled, sliced_type>>
+    constexpr Ret operator[](size_type idx) const
+    {
+        Expects(idx < bounds_.size()); // index is out of bounds of the array
+        const size_type ridx = idx * bounds_.stride();
+
+        // index is out of bounds of the underlying data
+        Expects(ridx < bounds_.total_size());
+        return {data_ + ridx, bounds_.slice().total_size(), bounds_.slice()};
+    }
+
+    constexpr bounds_type bounds() const noexcept { return bounds_; }
+
+    template <size_t Dim = 0>
+    constexpr size_type extent() const noexcept
+    {
+        static_assert(Dim < Rank,
+                      "dimension should be less than Rank (dimension count starts from 0)");
+        return bounds_.template extent<Dim>();
+    }
+
+    constexpr size_type size() const noexcept { return bounds_.size(); }
+
+    constexpr pointer data() const noexcept { return data_; }
+
+    constexpr explicit operator bool() const noexcept { return data_ != nullptr; }
+
+    constexpr iterator begin() const { return iterator{this, true}; }
+
+    constexpr iterator end() const { return iterator{this, false}; }
+
+    constexpr const_iterator cbegin() const
+    {
+        return const_iterator{reinterpret_cast<const const_strided_span*>(this), true};
+    }
+
+    constexpr const_iterator cend() const
+    {
+        return const_iterator{reinterpret_cast<const const_strided_span*>(this), false};
+    }
+
+    constexpr reverse_iterator rbegin() const { return reverse_iterator{end()}; }
+
+    constexpr reverse_iterator rend() const { return reverse_iterator{begin()}; }
+
+    constexpr const_reverse_iterator crbegin() const { return const_reverse_iterator{cend()}; }
+
+    constexpr const_reverse_iterator crend() const { return const_reverse_iterator{cbegin()}; }
+
+    template <typename OtherValueType, std::ptrdiff_t OtherRank,
+              typename Dummy = std::enable_if_t<std::is_same<
+                  std::remove_cv_t<value_type>, std::remove_cv_t<OtherValueType>>::value>>
+    constexpr bool operator==(const strided_span<OtherValueType, OtherRank>& other) const noexcept
+    {
+        return bounds_.size() == other.bounds_.size() &&
+               (data_ == other.data_ || std::equal(this->begin(), this->end(), other.begin()));
+    }
+
+    template <typename OtherValueType, std::ptrdiff_t OtherRank,
+              typename Dummy = std::enable_if_t<std::is_same<
+                  std::remove_cv_t<value_type>, std::remove_cv_t<OtherValueType>>::value>>
+    constexpr bool operator!=(const strided_span<OtherValueType, OtherRank>& other) const noexcept
+    {
+        return !(*this == other);
+    }
+
+    template <typename OtherValueType, std::ptrdiff_t OtherRank,
+              typename Dummy = std::enable_if_t<std::is_same<
+                  std::remove_cv_t<value_type>, std::remove_cv_t<OtherValueType>>::value>>
+    constexpr bool operator<(const strided_span<OtherValueType, OtherRank>& other) const noexcept
+    {
+        return std::lexicographical_compare(this->begin(), this->end(), other.begin(), other.end());
+    }
+
+    template <typename OtherValueType, std::ptrdiff_t OtherRank,
+              typename Dummy = std::enable_if_t<std::is_same<
+                  std::remove_cv_t<value_type>, std::remove_cv_t<OtherValueType>>::value>>
+    constexpr bool operator<=(const strided_span<OtherValueType, OtherRank>& other) const noexcept
+    {
+        return !(other < *this);
+    }
+
+    template <typename OtherValueType, std::ptrdiff_t OtherRank,
+              typename Dummy = std::enable_if_t<std::is_same<
+                  std::remove_cv_t<value_type>, std::remove_cv_t<OtherValueType>>::value>>
+    constexpr bool operator>(const strided_span<OtherValueType, OtherRank>& other) const noexcept
+    {
+        return (other < *this);
+    }
+
+    template <typename OtherValueType, std::ptrdiff_t OtherRank,
+              typename Dummy = std::enable_if_t<std::is_same<
+                  std::remove_cv_t<value_type>, std::remove_cv_t<OtherValueType>>::value>>
+    constexpr bool operator>=(const strided_span<OtherValueType, OtherRank>& other) const noexcept
+    {
+        return !(*this < other);
+    }
+
+private:
+    static index_type resize_extent(const index_type& extent, std::ptrdiff_t d)
+    {
+        // The last dimension of the array needs to contain a multiple of new type elements
+        Expects(extent[Rank - 1] >= d && (extent[Rank - 1] % d == 0));
+
+        index_type ret = extent;
+        ret[Rank - 1] /= d;
+
+        return ret;
+    }
+
+    template <bool Enabled = (Rank == 1), typename Dummy = std::enable_if_t<Enabled>>
+    static index_type resize_stride(const index_type& strides, std::ptrdiff_t, void* = 0)
+    {
+        // Only strided arrays with regular strides can be resized
+        Expects(strides[Rank - 1] == 1);
+
+        return strides;
+    }
+
+    template <bool Enabled = (Rank > 1), typename Dummy = std::enable_if_t<Enabled>>
+    static index_type resize_stride(const index_type& strides, std::ptrdiff_t d)
+    {
+        // Only strided arrays with regular strides can be resized
+        Expects(strides[Rank - 1] == 1);
+        // The strides must have contiguous chunks of
+        // memory that can contain a multiple of new type elements
+        Expects(strides[Rank - 2] >= d && (strides[Rank - 2] % d == 0));
+
+        for (size_t i = Rank - 1; i > 0; --i) {
+            // Only strided arrays with regular strides can be resized
+            Expects((strides[i - 1] >= strides[i]) && (strides[i - 1] % strides[i] == 0));
+        }
+
+        index_type ret = strides / d;
+        ret[Rank - 1] = 1;
+
+        return ret;
+    }
+};
+
+template <class Span>
+class contiguous_span_iterator
+    : public std::iterator<std::random_access_iterator_tag, typename Span::value_type>
+{
+    using Base = std::iterator<std::random_access_iterator_tag, typename Span::value_type>;
+
+public:
+    using typename Base::reference;
+    using typename Base::pointer;
+    using typename Base::difference_type;
+
+private:
+    template <typename ValueType, std::ptrdiff_t FirstDimension, std::ptrdiff_t... RestDimensions>
+    friend class multi_span;
+
+    pointer data_;
+    const Span* m_validator;
+    void validateThis() const
+    {
+        // iterator is out of range of the array
+        Expects(data_ >= m_validator->data_ && data_ < m_validator->data_ + m_validator->size());
+    }
+    contiguous_span_iterator(const Span* container, bool isbegin)
+        : data_(isbegin ? container->data_ : container->data_ + container->size())
+        , m_validator(container)
+    {
+    }
+
+public:
+    reference operator*() const noexcept
+    {
+        validateThis();
+        return *data_;
+    }
+    pointer operator->() const noexcept
+    {
+        validateThis();
+        return data_;
+    }
+    contiguous_span_iterator& operator++() noexcept
+    {
+        ++data_;
+        return *this;
+    }
+    contiguous_span_iterator operator++(int) noexcept
+    {
+        auto ret = *this;
+        ++(*this);
+        return ret;
+    }
+    contiguous_span_iterator& operator--() noexcept
+    {
+        --data_;
+        return *this;
+    }
+    contiguous_span_iterator operator--(int) noexcept
+    {
+        auto ret = *this;
+        --(*this);
+        return ret;
+    }
+    contiguous_span_iterator operator+(difference_type n) const noexcept
+    {
+        contiguous_span_iterator ret{*this};
+        return ret += n;
+    }
+    contiguous_span_iterator& operator+=(difference_type n) noexcept
+    {
+        data_ += n;
+        return *this;
+    }
+    contiguous_span_iterator operator-(difference_type n) const noexcept
+    {
+        contiguous_span_iterator ret{*this};
+        return ret -= n;
+    }
+    contiguous_span_iterator& operator-=(difference_type n) noexcept { return *this += -n; }
+    difference_type operator-(const contiguous_span_iterator& rhs) const noexcept
+    {
+        Expects(m_validator == rhs.m_validator);
+        return data_ - rhs.data_;
+    }
+    reference operator[](difference_type n) const noexcept { return *(*this + n); }
+    bool operator==(const contiguous_span_iterator& rhs) const noexcept
+    {
+        Expects(m_validator == rhs.m_validator);
+        return data_ == rhs.data_;
+    }
+    bool operator!=(const contiguous_span_iterator& rhs) const noexcept { return !(*this == rhs); }
+    bool operator<(const contiguous_span_iterator& rhs) const noexcept
+    {
+        Expects(m_validator == rhs.m_validator);
+        return data_ < rhs.data_;
+    }
+    bool operator<=(const contiguous_span_iterator& rhs) const noexcept { return !(rhs < *this); }
+    bool operator>(const contiguous_span_iterator& rhs) const noexcept { return rhs < *this; }
+    bool operator>=(const contiguous_span_iterator& rhs) const noexcept { return !(rhs > *this); }
+    void swap(contiguous_span_iterator& rhs) noexcept
+    {
+        std::swap(data_, rhs.data_);
+        std::swap(m_validator, rhs.m_validator);
+    }
+};
+
+template <typename Span>
+contiguous_span_iterator<Span> operator+(typename contiguous_span_iterator<Span>::difference_type n,
+                                         const contiguous_span_iterator<Span>& rhs) noexcept
+{
+    return rhs + n;
+}
+
+template <typename Span>
+class general_span_iterator
+    : public std::iterator<std::random_access_iterator_tag, typename Span::value_type>
+{
+    using Base = std::iterator<std::random_access_iterator_tag, typename Span::value_type>;
+
+public:
+    using typename Base::reference;
+    using typename Base::pointer;
+    using typename Base::difference_type;
+    using typename Base::value_type;
+
+private:
+    template <typename ValueType, size_t Rank>
+    friend class strided_span;
+
+    const Span* m_container;
+    typename Span::bounds_type::iterator m_itr;
+    general_span_iterator(const Span* container, bool isbegin)
+        : m_container(container)
+        , m_itr(isbegin ? m_container->bounds().begin() : m_container->bounds().end())
+    {
+    }
+
+public:
+    reference operator*() noexcept { return (*m_container)[*m_itr]; }
+    pointer operator->() noexcept { return &(*m_container)[*m_itr]; }
+    general_span_iterator& operator++() noexcept
+    {
+        ++m_itr;
+        return *this;
+    }
+    general_span_iterator operator++(int) noexcept
+    {
+        auto ret = *this;
+        ++(*this);
+        return ret;
+    }
+    general_span_iterator& operator--() noexcept
+    {
+        --m_itr;
+        return *this;
+    }
+    general_span_iterator operator--(int) noexcept
+    {
+        auto ret = *this;
+        --(*this);
+        return ret;
+    }
+    general_span_iterator operator+(difference_type n) const noexcept
+    {
+        general_span_iterator ret{*this};
+        return ret += n;
+    }
+    general_span_iterator& operator+=(difference_type n) noexcept
+    {
+        m_itr += n;
+        return *this;
+    }
+    general_span_iterator operator-(difference_type n) const noexcept
+    {
+        general_span_iterator ret{*this};
+        return ret -= n;
+    }
+    general_span_iterator& operator-=(difference_type n) noexcept { return *this += -n; }
+    difference_type operator-(const general_span_iterator& rhs) const noexcept
+    {
+        Expects(m_container == rhs.m_container);
+        return m_itr - rhs.m_itr;
+    }
+    value_type operator[](difference_type n) const noexcept { return (*m_container)[m_itr[n]]; }
+
+    bool operator==(const general_span_iterator& rhs) const noexcept
+    {
+        Expects(m_container == rhs.m_container);
+        return m_itr == rhs.m_itr;
+    }
+    bool operator!=(const general_span_iterator& rhs) const noexcept { return !(*this == rhs); }
+    bool operator<(const general_span_iterator& rhs) const noexcept
+    {
+        Expects(m_container == rhs.m_container);
+        return m_itr < rhs.m_itr;
+    }
+    bool operator<=(const general_span_iterator& rhs) const noexcept { return !(rhs < *this); }
+    bool operator>(const general_span_iterator& rhs) const noexcept { return rhs < *this; }
+    bool operator>=(const general_span_iterator& rhs) const noexcept { return !(rhs > *this); }
+    void swap(general_span_iterator& rhs) noexcept
+    {
+        std::swap(m_itr, rhs.m_itr);
+        std::swap(m_container, rhs.m_container);
+    }
+};
+
+template <typename Span>
+general_span_iterator<Span> operator+(typename general_span_iterator<Span>::difference_type n,
+                                      const general_span_iterator<Span>& rhs) noexcept
+{
+    return rhs + n;
+}
+
+} // namespace gsl
+
+#ifdef _MSC_VER
+
+#undef constexpr
+#pragma pop_macro("constexpr")
+
+#if _MSC_VER <= 1800
+#pragma warning(pop)
+
+#ifndef GSL_THROW_ON_CONTRACT_VIOLATION
+#undef noexcept
+#pragma pop_macro("noexcept")
+#endif // GSL_THROW_ON_CONTRACT_VIOLATION
+
+#undef GSL_MSVC_HAS_VARIADIC_CTOR_BUG
+
+#endif // _MSC_VER <= 1800
+
+#endif // _MSC_VER
+
+#if defined(GSL_THROW_ON_CONTRACT_VIOLATION)
+
+#undef noexcept
+
+#ifdef _MSC_VER
+#pragma warning(pop)
+#pragma pop_macro("noexcept")
+#endif
+
+#endif // GSL_THROW_ON_CONTRACT_VIOLATION
+
+#endif // GSL_MULTI_SPAN_H
diff --git a/include/span.h b/include/span.h
index b7a3d77..1405aa9 100644
--- a/include/span.h
+++ b/include/span.h
@@ -1,3 +1,4 @@
+
 ///////////////////////////////////////////////////////////////////////////////
 //
 // Copyright (c) 2015 Microsoft Corporation. All rights reserved.
@@ -20,17 +21,11 @@
 #define GSL_SPAN_H
 
 #include "gsl_assert.h"
+#include "gsl_byte.h"
 #include "gsl_util.h"
-#include <algorithm>
 #include <array>
-#include <cassert>
-#include <cstddef>
-#include <cstdint>
-#include <functional>
 #include <iterator>
 #include <limits>
-#include <new>
-#include <numeric>
 #include <stdexcept>
 #include <type_traits>
 #include <utility>
@@ -45,7 +40,7 @@
 // blanket turn off warnings from CppCoreCheck for now
 // so people aren't annoyed by them when running the tool.
 // more targeted suppressions will be added in a future update to the GSL
-#pragma warning(disable: 26481 26482 26483 26485 26490 26491 26492 26493 26495)
+#pragma warning(disable : 26481 26482 26483 26485 26490 26491 26492 26493 26495)
 
 // No MSVC does constexpr fully yet
 #pragma push_macro("constexpr")
@@ -55,14 +50,18 @@
 #if _MSC_VER <= 1800
 
 #define GSL_MSVC_HAS_VARIADIC_CTOR_BUG
-#define GSL_MSVC_NO_SUPPORT_FOR_MOVE_CTOR_DEFAULT
+#define GSL_MSVC_NO_DEFAULT_MOVE_CTOR
+#define GSL_MSVC_NO_CPP14_STD_EQUAL
 
-// noexcept is not understood 
+// noexcept is not understood
 #ifndef GSL_THROW_ON_CONTRACT_VIOLATION
 #pragma push_macro("noexcept")
 #define noexcept /* nothing */
 #endif
 
+#pragma push_macro("alignof")
+#define alignof __alignof
+
 // turn off some misguided warnings
 #pragma warning(push)
 #pragma warning(disable : 4351) // warns about newly introduced aggregate initializer behavior
@@ -85,2116 +84,708 @@
 namespace gsl
 {
 
-/*
-** begin definitions of index and bounds
-*/
-namespace details
-{
-    template <typename SizeType>
-    struct SizeTypeTraits
-    {
-        static const SizeType max_value = std::numeric_limits<SizeType>::max();
-    };
+// [views.constants], constants
+constexpr const std::ptrdiff_t dynamic_extent = -1;
 
-    template <typename... Ts>
-    class are_integral : public std::integral_constant<bool, true>
-    {
-    };
-
-    template <typename T, typename... Ts>
-    class are_integral<T, Ts...>
-        : public std::integral_constant<bool,
-                                        std::is_integral<T>::value && are_integral<Ts...>::value>
-    {
-    };
-}
-
-template <size_t Rank>
-class index final
-{
-    static_assert(Rank > 0, "Rank must be greater than 0!");
-
-    template <size_t OtherRank>
-    friend class index;
-
-public:
-    static const size_t rank = Rank;
-    using value_type = std::ptrdiff_t;
-    using size_type = value_type;
-    using reference = std::add_lvalue_reference_t<value_type>;
-    using const_reference = std::add_lvalue_reference_t<std::add_const_t<value_type>>;
-
-    constexpr index() noexcept {}
-
-    constexpr index(const value_type (&values)[Rank]) noexcept
-    {
-        std::copy(values, values + Rank, elems);
-    }
-
-#ifdef GSL_MSVC_HAS_VARIADIC_CTOR_BUG
-    template <
-        typename T, typename... Ts,
-        typename = std::enable_if_t<((sizeof...(Ts) + 1) == Rank) && std::is_integral<T>::value &&
-                                    details::are_integral<Ts...>::value>>
-    constexpr index(T t, Ts... ds)
-        : index({narrow_cast<value_type>(t), narrow_cast<value_type>(ds)...})
-    {
-    }
-#else
-    template <typename... Ts, typename = std::enable_if_t<(sizeof...(Ts) == Rank) &&
-                                                          details::are_integral<Ts...>::value>>
-    constexpr index(Ts... ds) noexcept : elems{narrow_cast<value_type>(ds)...}
-    {
-    }
-#endif
-
-    constexpr index(const index& other) noexcept = default;
-
-    constexpr index& operator=(const index& rhs) noexcept = default;
-
-    // Preconditions: component_idx < rank
-    constexpr reference operator[](size_t component_idx)
-    {
-        Expects(component_idx < Rank); // Component index must be less than rank
-        return elems[component_idx];
-    }
-
-    // Preconditions: component_idx < rank
-    constexpr const_reference operator[](size_t component_idx) const noexcept
-    {
-        Expects(component_idx < Rank); // Component index must be less than rank
-        return elems[component_idx];
-    }
-
-    constexpr bool operator==(const index& rhs) const noexcept
-    {
-        return std::equal(elems, elems + rank, rhs.elems);
-    }
-
-    constexpr bool operator!=(const index& rhs) const noexcept { return !(this == rhs); }
-
-    constexpr index operator+() const noexcept { return *this; }
-
-    constexpr index operator-() const noexcept
-    {
-        index ret = *this;
-        std::transform(ret, ret + rank, ret, std::negate<value_type>{});
-        return ret;
-    }
-
-    constexpr index operator+(const index& rhs) const noexcept
-    {
-        index ret = *this;
-        ret += rhs;
-        return ret;
-    }
-
-    constexpr index operator-(const index& rhs) const noexcept
-    {
-        index ret = *this;
-        ret -= rhs;
-        return ret;
-    }
-
-    constexpr index& operator+=(const index& rhs) noexcept
-    {
-        std::transform(elems, elems + rank, rhs.elems, elems, std::plus<value_type>{});
-        return *this;
-    }
-
-    constexpr index& operator-=(const index& rhs) noexcept
-    {
-        std::transform(elems, elems + rank, rhs.elems, elems, std::minus<value_type>{});
-        return *this;
-    }
-
-    constexpr index operator*(value_type v) const noexcept
-    {
-        index ret = *this;
-        ret *= v;
-        return ret;
-    }
-
-    constexpr index operator/(value_type v) const noexcept
-    {
-        index ret = *this;
-        ret /= v;
-        return ret;
-    }
-
-    friend constexpr index operator*(value_type v, const index& rhs) noexcept
-    {
-        return rhs * v;
-    }
-
-    constexpr index& operator*=(value_type v) noexcept
-    {
-        std::transform(elems, elems + rank, elems,
-                       [v](value_type x) { return std::multiplies<value_type>{}(x, v); });
-        return *this;
-    }
-
-    constexpr index& operator/=(value_type v) noexcept
-    {
-        std::transform(elems, elems + rank, elems,
-                       [v](value_type x) { return std::divides<value_type>{}(x, v); });
-        return *this;
-    }
-
-private:
-    value_type elems[Rank] = {};
-};
-
-#ifndef _MSC_VER
-
-struct static_bounds_dynamic_range_t
-{
-    template <typename T, typename Dummy = std::enable_if_t<std::is_integral<T>::value>>
-    constexpr operator T() const noexcept
-    {
-        return narrow_cast<T>(-1);
-    }
-
-    template <typename T, typename Dummy = std::enable_if_t<std::is_integral<T>::value>>
-    constexpr bool operator==(T other) const noexcept
-    {
-        return narrow_cast<T>(-1) == other;
-    }
-
-    template <typename T, typename Dummy = std::enable_if_t<std::is_integral<T>::value>>
-    constexpr bool operator!=(T other) const noexcept
-    {
-        return narrow_cast<T>(-1) != other;
-    }
-};
-
-template <typename T, typename Dummy = std::enable_if_t<std::is_integral<T>::value>>
-constexpr bool operator==(T left, static_bounds_dynamic_range_t right) noexcept
-{
-    return right == left;
-}
-
-template <typename T, typename Dummy = std::enable_if_t<std::is_integral<T>::value>>
-constexpr bool operator!=(T left, static_bounds_dynamic_range_t right) noexcept
-{
-    return right != left;
-}
-
-constexpr static_bounds_dynamic_range_t dynamic_range{};
-#else
-const std::ptrdiff_t dynamic_range = -1;
-#endif
-
-struct generalized_mapping_tag
-{
-};
-struct contiguous_mapping_tag : generalized_mapping_tag
-{
-};
-
-namespace details
-{
-
-    template <std::ptrdiff_t Left, std::ptrdiff_t Right>
-    struct LessThan
-    {
-        static const bool value = Left < Right;
-    };
-
-    template <std::ptrdiff_t... Ranges>
-    struct BoundsRanges
-    {
-        using size_type = std::ptrdiff_t;
-        static const size_type Depth = 0;
-        static const size_type DynamicNum = 0;
-        static const size_type CurrentRange = 1;
-        static const size_type TotalSize = 1;
-
-        // TODO : following signature is for work around VS bug
-        template <typename OtherRange>
-        BoundsRanges(const OtherRange&, bool /* firstLevel */)
-        {
-        }
-
-        BoundsRanges(const BoundsRanges&) = default;
-        BoundsRanges& operator=(const BoundsRanges&) = default;
-        BoundsRanges(const std::ptrdiff_t* const) {}
-        BoundsRanges() = default;
-
-        template <typename T, size_t Dim>
-        void serialize(T&) const
-        {
-        }
-
-        template <typename T, size_t Dim>
-        size_type linearize(const T&) const
-        {
-            return 0;
-        }
-
-        template <typename T, size_t Dim>
-        size_type contains(const T&) const
-        {
-            return -1;
-        }
-
-        size_type elementNum(size_t) const noexcept { return 0; }
-
-        size_type totalSize() const noexcept { return TotalSize; }
-
-        bool operator==(const BoundsRanges&) const noexcept { return true; }
-    };
-
-    template <std::ptrdiff_t... RestRanges>
-    struct BoundsRanges<dynamic_range, RestRanges...> : BoundsRanges<RestRanges...>
-    {
-        using Base = BoundsRanges<RestRanges...>;
-        using size_type = std::ptrdiff_t;
-        static const size_t Depth = Base::Depth + 1;
-        static const size_t DynamicNum = Base::DynamicNum + 1;
-        static const size_type CurrentRange = dynamic_range;
-        static const size_type TotalSize = dynamic_range;
-        const size_type m_bound;
-
-        BoundsRanges(const BoundsRanges&) = default;
-
-        BoundsRanges(const std::ptrdiff_t* const arr)
-            : Base(arr + 1), m_bound(*arr * this->Base::totalSize())
-        {
-            Expects(0 <= *arr);
-        }
-
-        BoundsRanges() : m_bound(0) {}
-
-        template <std::ptrdiff_t OtherRange, std::ptrdiff_t... RestOtherRanges>
-        BoundsRanges(const BoundsRanges<OtherRange, RestOtherRanges...>& other,
-                     bool /* firstLevel */ = true)
-            : Base(static_cast<const BoundsRanges<RestOtherRanges...>&>(other), false)
-            , m_bound(other.totalSize())
-        {
-        }
-
-        template <typename T, size_t Dim = 0>
-        void serialize(T& arr) const
-        {
-            arr[Dim] = elementNum();
-            this->Base::template serialize<T, Dim + 1>(arr);
-        }
-
-        template <typename T, size_t Dim = 0>
-        size_type linearize(const T& arr) const
-        {
-            const size_type index = this->Base::totalSize() * arr[Dim];
-            Expects(index < m_bound);
-            return index + this->Base::template linearize<T, Dim + 1>(arr);
-        }
-
-        template <typename T, size_t Dim = 0>
-        size_type contains(const T& arr) const
-        {
-            const ptrdiff_t last = this->Base::template contains<T, Dim + 1>(arr);
-            if (last == -1) return -1;
-            const ptrdiff_t cur = this->Base::totalSize() * arr[Dim];
-            return cur < m_bound ? cur + last : -1;
-        }
-
-        size_type totalSize() const noexcept { return m_bound; }
-
-        size_type elementNum() const noexcept { return totalSize() / this->Base::totalSize(); }
-
-        size_type elementNum(size_t dim) const noexcept
-        {
-            if (dim > 0)
-                return this->Base::elementNum(dim - 1);
-            else
-                return elementNum();
-        }
-
-        bool operator==(const BoundsRanges& rhs) const noexcept
-        {
-            return m_bound == rhs.m_bound &&
-                   static_cast<const Base&>(*this) == static_cast<const Base&>(rhs);
-        }
-    };
-
-    template <std::ptrdiff_t CurRange, std::ptrdiff_t... RestRanges>
-    struct BoundsRanges<CurRange, RestRanges...> : BoundsRanges<RestRanges...>
-    {
-        using Base = BoundsRanges<RestRanges...>;
-        using size_type = std::ptrdiff_t;
-        static const size_t Depth = Base::Depth + 1;
-        static const size_t DynamicNum = Base::DynamicNum;
-        static const size_type CurrentRange = CurRange;
-        static const size_type TotalSize =
-            Base::TotalSize == dynamic_range ? dynamic_range : CurrentRange * Base::TotalSize;
-
-        BoundsRanges(const BoundsRanges&) = default;
-
-        BoundsRanges(const std::ptrdiff_t* const arr) : Base(arr) {}
-        BoundsRanges() = default;
-
-        template <std::ptrdiff_t OtherRange, std::ptrdiff_t... RestOtherRanges>
-        BoundsRanges(const BoundsRanges<OtherRange, RestOtherRanges...>& other,
-                     bool firstLevel = true)
-            : Base(static_cast<const BoundsRanges<RestOtherRanges...>&>(other), false)
-        {
-            (void) firstLevel;
-        }
-
-        template <typename T, size_t Dim = 0>
-        void serialize(T& arr) const
-        {
-            arr[Dim] = elementNum();
-            this->Base::template serialize<T, Dim + 1>(arr);
-        }
-
-        template <typename T, size_t Dim = 0>
-        size_type linearize(const T& arr) const
-        {
-            Expects(arr[Dim] < CurrentRange); // Index is out of range
-            return this->Base::totalSize() * arr[Dim] +
-                   this->Base::template linearize<T, Dim + 1>(arr);
-        }
-
-        template <typename T, size_t Dim = 0>
-        size_type contains(const T& arr) const
-        {
-            if (arr[Dim] >= CurrentRange) return -1;
-            const size_type last = this->Base::template contains<T, Dim + 1>(arr);
-            if (last == -1) return -1;
-            return this->Base::totalSize() * arr[Dim] + last;
-        }
-
-        size_type totalSize() const noexcept { return CurrentRange * this->Base::totalSize(); }
-
-        size_type elementNum() const noexcept { return CurrentRange; }
-
-        size_type elementNum(size_t dim) const noexcept
-        {
-            if (dim > 0)
-                return this->Base::elementNum(dim - 1);
-            else
-                return elementNum();
-        }
-
-        bool operator==(const BoundsRanges& rhs) const noexcept
-        {
-            return static_cast<const Base&>(*this) == static_cast<const Base&>(rhs);
-        }
-    };
-
-    template <typename SourceType, typename TargetType>
-    struct BoundsRangeConvertible
-        : public std::integral_constant<bool, (SourceType::TotalSize >= TargetType::TotalSize ||
-                                               TargetType::TotalSize == dynamic_range ||
-                                               SourceType::TotalSize == dynamic_range ||
-                                               TargetType::TotalSize == 0)>
-    {
-    };
-
-    template <typename TypeChain>
-    struct TypeListIndexer
-    {
-        const TypeChain& obj_;
-        TypeListIndexer(const TypeChain& obj) : obj_(obj) {}
-
-        template <size_t N>
-        const TypeChain& getObj(std::true_type)
-        {
-            return obj_;
-        }
-
-        template <size_t N, typename MyChain = TypeChain, typename MyBase = typename MyChain::Base>
-        auto getObj(std::false_type)
-            -> decltype(TypeListIndexer<MyBase>(static_cast<const MyBase&>(obj_)).template get<N>())
-        {
-            return TypeListIndexer<MyBase>(static_cast<const MyBase&>(obj_)).template get<N>();
-        }
-
-        template <size_t N>
-        auto get() -> decltype(getObj<N - 1>(std::integral_constant<bool, N == 0>()))
-        {
-            return getObj<N - 1>(std::integral_constant<bool, N == 0>());
-        }
-    };
-
-    template <typename TypeChain>
-    TypeListIndexer<TypeChain> createTypeListIndexer(const TypeChain& obj)
-    {
-        return TypeListIndexer<TypeChain>(obj);
-    }
-
-    template <size_t Rank, bool Enabled = (Rank > 1),
-              typename Ret = std::enable_if_t<Enabled, index<Rank - 1>>>
-    constexpr Ret shift_left(const index<Rank>& other) noexcept
-    {
-        Ret ret{};
-        for (size_t i = 0; i < Rank - 1; ++i) {
-            ret[i] = other[i + 1];
-        }
-        return ret;
-    }
-}
-
-template <typename IndexType>
-class bounds_iterator;
-
-template <std::ptrdiff_t... Ranges>
-class static_bounds
-{
-public:
-    static_bounds(const details::BoundsRanges<Ranges...>&) {}
-};
-
-template <std::ptrdiff_t FirstRange, std::ptrdiff_t... RestRanges>
-class static_bounds<FirstRange, RestRanges...>
-{
-    using MyRanges = details::BoundsRanges<FirstRange, RestRanges...>;
-
-    MyRanges m_ranges;
-    constexpr static_bounds(const MyRanges& range) : m_ranges(range) {}
-
-    template <std::ptrdiff_t... OtherRanges>
-    friend class static_bounds;
-
-public:
-    static const size_t rank = MyRanges::Depth;
-    static const size_t dynamic_rank = MyRanges::DynamicNum;
-    static const std::ptrdiff_t static_size = MyRanges::TotalSize;
-
-    using size_type = std::ptrdiff_t;
-    using index_type = index<rank>;
-    using const_index_type = std::add_const_t<index_type>;
-    using iterator = bounds_iterator<const_index_type>;
-    using const_iterator = bounds_iterator<const_index_type>;
-    using difference_type = std::ptrdiff_t;
-    using sliced_type = static_bounds<RestRanges...>;
-    using mapping_type = contiguous_mapping_tag;
-
-    constexpr static_bounds(const static_bounds&) = default;
-
-    template <typename SourceType, typename TargetType, size_t Rank>
-    struct BoundsRangeConvertible2;
-
-    template <size_t Rank, typename SourceType, typename TargetType,
-              typename Ret = BoundsRangeConvertible2<typename SourceType::Base,
-                                                     typename TargetType::Base, Rank>>
-    static auto helpBoundsRangeConvertible(SourceType, TargetType, std::true_type) -> Ret;
-
-    template <size_t Rank, typename SourceType, typename TargetType>
-    static auto helpBoundsRangeConvertible(SourceType, TargetType, ...) -> std::false_type;
-
-    template <typename SourceType, typename TargetType, size_t Rank>
-    struct BoundsRangeConvertible2
-        : decltype(helpBoundsRangeConvertible<Rank - 1>(
-              SourceType(), TargetType(),
-              std::integral_constant<bool,
-                                     SourceType::Depth == TargetType::Depth &&
-                                         (SourceType::CurrentRange == TargetType::CurrentRange ||
-                                          TargetType::CurrentRange == dynamic_range ||
-                                          SourceType::CurrentRange == dynamic_range)>()))
-    {
-    };
-
-    template <typename SourceType, typename TargetType>
-    struct BoundsRangeConvertible2<SourceType, TargetType, 0> : std::true_type
-    {
-    };
-
-    template <typename SourceType, typename TargetType, std::ptrdiff_t Rank = TargetType::Depth>
-    struct BoundsRangeConvertible
-        : decltype(helpBoundsRangeConvertible<Rank - 1>(
-              SourceType(), TargetType(),
-              std::integral_constant<bool,
-                                     SourceType::Depth == TargetType::Depth &&
-                                         (!details::LessThan<SourceType::CurrentRange,
-                                                             TargetType::CurrentRange>::value ||
-                                          TargetType::CurrentRange == dynamic_range ||
-                                          SourceType::CurrentRange == dynamic_range)>()))
-    {
-    };
-
-    template <typename SourceType, typename TargetType>
-    struct BoundsRangeConvertible<SourceType, TargetType, 0> : std::true_type
-    {
-    };
-
-    template <std::ptrdiff_t... Ranges,
-              typename = std::enable_if_t<details::BoundsRangeConvertible<
-                  details::BoundsRanges<Ranges...>,
-                  details::BoundsRanges<FirstRange, RestRanges...>>::value>>
-    constexpr static_bounds(const static_bounds<Ranges...>& other) : m_ranges(other.m_ranges)
-    {
-        Expects((MyRanges::DynamicNum == 0 && details::BoundsRanges<Ranges...>::DynamicNum == 0) ||
-                MyRanges::DynamicNum > 0 || other.m_ranges.totalSize() >= m_ranges.totalSize());
-    }
-
-    constexpr static_bounds(std::initializer_list<size_type> il)
-        : m_ranges(static_cast<const std::ptrdiff_t*>(il.begin()))
-    {
-        // Size of the initializer list must match the rank of the array
-        Expects((MyRanges::DynamicNum == 0 && il.size() == 1 && *il.begin() == static_size) ||
-                MyRanges::DynamicNum == il.size());
-        // Size of the range must be less than the max element of the size type
-        Expects(m_ranges.totalSize() <= PTRDIFF_MAX);
-    }
-
-    constexpr static_bounds() = default;
-
-    constexpr static_bounds& operator=(const static_bounds& otherBounds)
-    {
-        new (&m_ranges) MyRanges(otherBounds.m_ranges);
-        return *this;
-    }
-
-    constexpr sliced_type slice() const noexcept
-    {
-        return sliced_type{static_cast<const details::BoundsRanges<RestRanges...>&>(m_ranges)};
-    }
-
-    constexpr size_type stride() const noexcept { return rank > 1 ? slice().size() : 1; }
-
-    constexpr size_type size() const noexcept { return m_ranges.totalSize(); }
-
-    constexpr size_type total_size() const noexcept { return m_ranges.totalSize(); }
-
-    constexpr size_type linearize(const index_type& idx) const { return m_ranges.linearize(idx); }
-
-    constexpr bool contains(const index_type& idx) const noexcept
-    {
-        return m_ranges.contains(idx) != -1;
-    }
-
-    constexpr size_type operator[](size_t index) const noexcept
-    {
-        return m_ranges.elementNum(index);
-    }
-
-    template <size_t Dim = 0>
-    constexpr size_type extent() const noexcept
-    {
-        static_assert(Dim < rank,
-                      "dimension should be less than rank (dimension count starts from 0)");
-        return details::createTypeListIndexer(m_ranges).template get<Dim>().elementNum();
-    }
-
-    template <typename IntType>
-    constexpr size_type extent(IntType dim) const noexcept
-    {
-        static_assert(std::is_integral<IntType>::value,
-                      "Dimension parameter must be supplied as an integral type.");
-        auto real_dim = narrow_cast<size_t>(dim);
-        Expects(real_dim < rank);
-
-        return m_ranges.elementNum(real_dim);
-    }
-
-    constexpr index_type index_bounds() const noexcept
-    {
-        size_type extents[rank] = {};
-        m_ranges.serialize(extents);
-        return {extents};
-    }
-
-    template <std::ptrdiff_t... Ranges>
-    constexpr bool operator==(const static_bounds<Ranges...>& rhs) const noexcept
-    {
-        return this->size() == rhs.size();
-    }
-
-    template <std::ptrdiff_t... Ranges>
-    constexpr bool operator!=(const static_bounds<Ranges...>& rhs) const noexcept
-    {
-        return !(*this == rhs);
-    }
-
-    constexpr const_iterator begin() const noexcept { return const_iterator(*this, index_type{}); }
-
-    constexpr const_iterator end() const noexcept
-    {
-        return const_iterator(*this, this->index_bounds());
-    }
-};
-
-template <size_t Rank>
-class strided_bounds
-{
-    template <size_t OtherRank>
-    friend class strided_bounds;
-
-public:
-    static const size_t rank = Rank;
-    using value_type = std::ptrdiff_t;
-    using reference = std::add_lvalue_reference_t<value_type>;
-    using const_reference = std::add_const_t<reference>;
-    using size_type = value_type;
-    using difference_type = value_type;
-    using index_type = index<rank>;
-    using const_index_type = std::add_const_t<index_type>;
-    using iterator = bounds_iterator<const_index_type>;
-    using const_iterator = bounds_iterator<const_index_type>;
-    static const value_type dynamic_rank = rank;
-    static const value_type static_size = dynamic_range;
-    using sliced_type = std::conditional_t<rank != 0, strided_bounds<rank - 1>, void>;
-    using mapping_type = generalized_mapping_tag;
-
-    constexpr strided_bounds(const strided_bounds&) noexcept = default;
-
-    constexpr strided_bounds& operator=(const strided_bounds&) noexcept = default;
-
-    constexpr strided_bounds(const value_type (&values)[rank], index_type strides)
-        : m_extents(values), m_strides(std::move(strides))
-    {
-    }
-
-    constexpr strided_bounds(const index_type& extents, const index_type& strides) noexcept
-        : m_extents(extents),
-          m_strides(strides)
-    {
-    }
-
-    constexpr index_type strides() const noexcept { return m_strides; }
-
-    constexpr size_type total_size() const noexcept
-    {
-        size_type ret = 0;
-        for (size_t i = 0; i < rank; ++i) {
-            ret += (m_extents[i] - 1) * m_strides[i];
-        }
-        return ret + 1;
-    }
-
-    constexpr size_type size() const noexcept
-    {
-        size_type ret = 1;
-        for (size_t i = 0; i < rank; ++i) {
-            ret *= m_extents[i];
-        }
-        return ret;
-    }
-
-    constexpr bool contains(const index_type& idx) const noexcept
-    {
-        for (size_t i = 0; i < rank; ++i) {
-            if (idx[i] < 0 || idx[i] >= m_extents[i]) return false;
-        }
-        return true;
-    }
-
-    constexpr size_type linearize(const index_type& idx) const noexcept
-    {
-        size_type ret = 0;
-        for (size_t i = 0; i < rank; i++) {
-            Expects(idx[i] < m_extents[i]); // index is out of bounds of the array
-            ret += idx[i] * m_strides[i];
-        }
-        return ret;
-    }
-
-    constexpr size_type stride() const noexcept { return m_strides[0]; }
-
-    template <bool Enabled = (rank > 1), typename Ret = std::enable_if_t<Enabled, sliced_type>>
-    constexpr sliced_type slice() const
-    {
-        return {details::shift_left(m_extents), details::shift_left(m_strides)};
-    }
-
-    template <size_t Dim = 0>
-    constexpr size_type extent() const noexcept
-    {
-        static_assert(Dim < Rank,
-                      "dimension should be less than rank (dimension count starts from 0)");
-        return m_extents[Dim];
-    }
-
-    constexpr index_type index_bounds() const noexcept { return m_extents; }
-    constexpr const_iterator begin() const noexcept { return const_iterator{*this, index_type{}}; }
-
-    constexpr const_iterator end() const noexcept { return const_iterator{*this, index_bounds()}; }
-
-private:
-    index_type m_extents;
-    index_type m_strides;
-};
-
-template <typename T>
-struct is_bounds : std::integral_constant<bool, false>
-{
-};
-template <std::ptrdiff_t... Ranges>
-struct is_bounds<static_bounds<Ranges...>> : std::integral_constant<bool, true>
-{
-};
-template <size_t Rank>
-struct is_bounds<strided_bounds<Rank>> : std::integral_constant<bool, true>
-{
-};
-
-template <typename IndexType>
-class bounds_iterator : public std::iterator<std::random_access_iterator_tag, IndexType>
-{
-private:
-    using Base = std::iterator<std::random_access_iterator_tag, IndexType>;
-
-public:
-    static const size_t rank = IndexType::rank;
-    using typename Base::reference;
-    using typename Base::pointer;
-    using typename Base::difference_type;
-    using typename Base::value_type;
-    using index_type = value_type;
-    using index_size_type = typename IndexType::value_type;
-    template <typename Bounds>
-    explicit bounds_iterator(const Bounds& bnd, value_type curr) noexcept
-        : boundary_(bnd.index_bounds()),
-          curr_(std::move(curr))
-    {
-        static_assert(is_bounds<Bounds>::value, "Bounds type must be provided");
-    }
-
-    constexpr reference operator*() const noexcept { return curr_; }
-
-    constexpr pointer operator->() const noexcept { return &curr_; }
-
-    constexpr bounds_iterator& operator++() noexcept
-    {
-        for (size_t i = rank; i-- > 0;) {
-            if (curr_[i] < boundary_[i] - 1) {
-                curr_[i]++;
-                return *this;
-            }
-            curr_[i] = 0;
-        }
-        // If we're here we've wrapped over - set to past-the-end.
-        curr_ = boundary_;
-        return *this;
-    }
-
-    constexpr bounds_iterator operator++(int) noexcept
-    {
-        auto ret = *this;
-        ++(*this);
-        return ret;
-    }
-
-    constexpr bounds_iterator& operator--() noexcept
-    {
-        if (!less(curr_, boundary_)) {
-            // if at the past-the-end, set to last element
-            for (size_t i = 0; i < rank; ++i) {
-                curr_[i] = boundary_[i] - 1;
-            }
-            return *this;
-        }
-        for (size_t i = rank; i-- > 0;) {
-            if (curr_[i] >= 1) {
-                curr_[i]--;
-                return *this;
-            }
-            curr_[i] = boundary_[i] - 1;
-        }
-        // If we're here the preconditions were violated
-        // "pre: there exists s such that r == ++s"
-        Expects(false);
-        return *this;
-    }
-
-    constexpr bounds_iterator operator--(int) noexcept
-    {
-        auto ret = *this;
-        --(*this);
-        return ret;
-    }
-
-    constexpr bounds_iterator operator+(difference_type n) const noexcept
-    {
-        bounds_iterator ret{*this};
-        return ret += n;
-    }
-
-    constexpr bounds_iterator& operator+=(difference_type n) noexcept
-    {
-        auto linear_idx = linearize(curr_) + n;
-        std::remove_const_t<value_type> stride = 0;
-        stride[rank - 1] = 1;
-        for (size_t i = rank - 1; i-- > 0;) {
-            stride[i] = stride[i + 1] * boundary_[i + 1];
-        }
-        for (size_t i = 0; i < rank; ++i) {
-            curr_[i] = linear_idx / stride[i];
-            linear_idx = linear_idx % stride[i];
-        }
-        // index is out of bounds of the array
-        Expects(!less(curr_, index_type{}) && !less(boundary_, curr_));
-        return *this;
-    }
-
-    constexpr bounds_iterator operator-(difference_type n) const noexcept
-    {
-        bounds_iterator ret{*this};
-        return ret -= n;
-    }
-
-    constexpr bounds_iterator& operator-=(difference_type n) noexcept { return * this += -n; }
-
-    constexpr difference_type operator-(const bounds_iterator& rhs) const noexcept
-    {
-        return linearize(curr_) - linearize(rhs.curr_);
-    }
-
-    constexpr value_type operator[](difference_type n) const noexcept { return *(*this + n); }
-
-    constexpr bool operator==(const bounds_iterator& rhs) const noexcept
-    {
-        return curr_ == rhs.curr_;
-    }
-
-    constexpr bool operator!=(const bounds_iterator& rhs) const noexcept { return !(*this == rhs); }
-
-    constexpr bool operator<(const bounds_iterator& rhs) const noexcept
-    {
-        return less(curr_, rhs.curr_);
-    }
-
-    constexpr bool operator<=(const bounds_iterator& rhs) const noexcept { return !(rhs < *this); }
-
-    constexpr bool operator>(const bounds_iterator& rhs) const noexcept { return rhs < *this; }
-
-    constexpr bool operator>=(const bounds_iterator& rhs) const noexcept { return !(rhs > *this); }
-
-    void swap(bounds_iterator& rhs) noexcept
-    {
-        std::swap(boundary_, rhs.boundary_);
-        std::swap(curr_, rhs.curr_);
-    }
-
-private:
-    constexpr bool less(index_type& one, index_type& other) const noexcept
-    {
-        for (size_t i = 0; i < rank; ++i) {
-            if (one[i] < other[i]) return true;
-        }
-        return false;
-    }
-
-    constexpr index_size_type linearize(const value_type& idx) const noexcept
-    {
-        // TODO: Smarter impl.
-        // Check if past-the-end
-        index_size_type multiplier = 1;
-        index_size_type res = 0;
-        if (!less(idx, boundary_)) {
-            res = 1;
-            for (size_t i = rank; i-- > 0;) {
-                res += (idx[i] - 1) * multiplier;
-                multiplier *= boundary_[i];
-            }
-        }
-        else
-        {
-            for (size_t i = rank; i-- > 0;) {
-                res += idx[i] * multiplier;
-                multiplier *= boundary_[i];
-            }
-        }
-        return res;
-    }
-
-    value_type boundary_;
-    std::remove_const_t<value_type> curr_;
-};
-
-template <typename IndexType>
-bounds_iterator<IndexType> operator+(typename bounds_iterator<IndexType>::difference_type n,
-                                     const bounds_iterator<IndexType>& rhs) noexcept
-{
-    return rhs + n;
-}
-
-namespace details
-{
-    template <typename Bounds>
-    constexpr std::enable_if_t<
-        std::is_same<typename Bounds::mapping_type, generalized_mapping_tag>::value,
-        typename Bounds::index_type>
-    make_stride(const Bounds& bnd) noexcept
-    {
-        return bnd.strides();
-    }
-
-    // Make a stride vector from bounds, assuming contiguous memory.
-    template <typename Bounds>
-    constexpr std::enable_if_t<
-        std::is_same<typename Bounds::mapping_type, contiguous_mapping_tag>::value,
-        typename Bounds::index_type>
-    make_stride(const Bounds& bnd) noexcept
-    {
-        auto extents = bnd.index_bounds();
-        typename Bounds::size_type stride[Bounds::rank] = {};
-
-        stride[Bounds::rank - 1] = 1;
-        for (size_t i = 1; i < Bounds::rank; ++i) {
-            stride[Bounds::rank - i - 1] = stride[Bounds::rank - i] * extents[Bounds::rank - i];
-        }
-        return {stride};
-    }
-
-    template <typename BoundsSrc, typename BoundsDest>
-    void verifyBoundsReshape(const BoundsSrc& src, const BoundsDest& dest)
-    {
-        static_assert(is_bounds<BoundsSrc>::value && is_bounds<BoundsDest>::value,
-                      "The src type and dest type must be bounds");
-        static_assert(std::is_same<typename BoundsSrc::mapping_type, contiguous_mapping_tag>::value,
-                      "The source type must be a contiguous bounds");
-        static_assert(BoundsDest::static_size == dynamic_range ||
-                          BoundsSrc::static_size == dynamic_range ||
-                          BoundsDest::static_size == BoundsSrc::static_size,
-                      "The source bounds must have same size as dest bounds");
-        Expects(src.size() == dest.size());
-    }
-
-} // namespace details
-
-template <typename Span>
-class contiguous_span_iterator;
-template <typename Span>
-class general_span_iterator;
-enum class byte : std::uint8_t
-{
-};
-
-template <std::ptrdiff_t DimSize = dynamic_range>
-struct dim
-{
-    static const std::ptrdiff_t value = DimSize;
-};
-template <>
-struct dim<dynamic_range>
-{
-    static const std::ptrdiff_t value = dynamic_range;
-    const std::ptrdiff_t dvalue;
-    dim(std::ptrdiff_t size) : dvalue(size) {}
-};
-
-template <typename ValueType, std::ptrdiff_t FirstDimension = dynamic_range,
-          std::ptrdiff_t... RestDimensions>
+template <class ElementType, std::ptrdiff_t Extent = dynamic_extent>
 class span;
 
-template <typename ValueType, size_t Rank>
-class strided_span;
-
+// implementation details
 namespace details
 {
-    template <typename T, typename = std::true_type>
-    struct SpanTypeTraits
-    {
-        using value_type = T;
-        using size_type = size_t;
-    };
-
-    template <typename Traits>
-    struct SpanTypeTraits<Traits, typename std::is_reference<typename Traits::span_traits&>::type>
-    {
-        using value_type = typename Traits::span_traits::value_type;
-        using size_type = typename Traits::span_traits::size_type;
-    };
-
-    template <typename T, std::ptrdiff_t... Ranks>
-    struct SpanArrayTraits
-    {
-        using type = span<T, Ranks...>;
-        using value_type = T;
-        using bounds_type = static_bounds<Ranks...>;
-        using pointer = T*;
-        using reference = T&;
-    };
-    template <typename T, std::ptrdiff_t N, std::ptrdiff_t... Ranks>
-    struct SpanArrayTraits<T[N], Ranks...> : SpanArrayTraits<T, Ranks..., N>
-    {
-    };
-
-    template <typename BoundsType>
-    BoundsType newBoundsHelperImpl(std::ptrdiff_t totalSize, std::true_type) // dynamic size
-    {
-        Expects(totalSize >= 0 && totalSize <= PTRDIFF_MAX);
-        return BoundsType{totalSize};
-    }
-    template <typename BoundsType>
-    BoundsType newBoundsHelperImpl(std::ptrdiff_t totalSize, std::false_type) // static size
-    {
-        Expects(BoundsType::static_size <= totalSize);
-        return {};
-    }
-    template <typename BoundsType>
-    BoundsType newBoundsHelper(std::ptrdiff_t totalSize)
-    {
-        static_assert(BoundsType::dynamic_rank <= 1, "dynamic rank must less or equal to 1");
-        return newBoundsHelperImpl<BoundsType>(
-            totalSize, std::integral_constant<bool, BoundsType::dynamic_rank == 1>());
-    }
-
-    struct Sep
-    {
-    };
-
-    template <typename T, typename... Args>
-    T static_as_span_helper(Sep, Args... args)
-    {
-        return T{narrow_cast<typename T::size_type>(args)...};
-    }
-    template <typename T, typename Arg, typename... Args>
-    std::enable_if_t<
-        !std::is_same<Arg, dim<dynamic_range>>::value && !std::is_same<Arg, Sep>::value, T>
-        static_as_span_helper(Arg, Args... args)
-    {
-        return static_as_span_helper<T>(args...);
-    }
-    template <typename T, typename... Args>
-    T static_as_span_helper(dim<dynamic_range> val, Args... args)
-    {
-        return static_as_span_helper<T>(args..., val.dvalue);
-    }
-
-    template <typename... Dimensions>
-    struct static_as_span_static_bounds_helper
-    {
-        using type = static_bounds<(Dimensions::value)...>;
-    };
-
-    template <typename T>
+    template <class T>
     struct is_span_oracle : std::false_type
     {
     };
 
-    template <typename ValueType, std::ptrdiff_t FirstDimension, std::ptrdiff_t... RestDimensions>
-    struct is_span_oracle<span<ValueType, FirstDimension, RestDimensions...>> : std::true_type
+    template <class ElementType, std::ptrdiff_t Extent>
+    struct is_span_oracle<gsl::span<ElementType, Extent>> : std::true_type
     {
     };
 
-    template <typename ValueType, std::ptrdiff_t Rank>
-    struct is_span_oracle<strided_span<ValueType, Rank>> : std::true_type
+    template <class T>
+    struct is_span : public is_span_oracle<std::remove_cv_t<T>>
     {
     };
 
-    template <typename T>
-    struct is_span : is_span_oracle<std::remove_cv_t<T>>
+    template <class T>
+    struct is_std_array_oracle : std::false_type
     {
     };
-}
 
-template <typename ValueType, std::ptrdiff_t FirstDimension, std::ptrdiff_t... RestDimensions>
+    template <class ElementType, size_t Extent>
+    struct is_std_array_oracle<std::array<ElementType, Extent>> : std::true_type
+    {
+    };
+
+    template <class T>
+    struct is_std_array : public is_std_array_oracle<std::remove_cv_t<T>>
+    {
+    };
+
+    template <class From, class To>
+    struct is_allowed_pointer_conversion
+        : public std::integral_constant<bool, std::is_pointer<From>::value &&
+                                                  std::is_pointer<To>::value &&
+                                                  std::is_convertible<From, To>::value>
+    {
+    };
+
+    template <class From, class To>
+    struct is_allowed_integral_conversion
+        : public std::integral_constant<
+              bool, std::is_integral<From>::value && std::is_integral<To>::value &&
+                        sizeof(From) == sizeof(To) && alignof(From) == alignof(To) &&
+                        std::is_convertible<From, To>::value>
+    {
+    };
+
+    template <std::ptrdiff_t From, std::ptrdiff_t To>
+    struct is_allowed_extent_conversion
+        : public std::integral_constant<bool, From == To || From == gsl::dynamic_extent ||
+                                                  To == gsl::dynamic_extent>
+    {
+    };
+
+    template <class From, class To>
+    struct is_allowed_element_type_conversion
+        : public std::integral_constant<bool, std::is_same<From, std::remove_cv_t<To>>::value ||
+                                                  is_allowed_pointer_conversion<From, To>::value ||
+                                                  is_allowed_integral_conversion<From, To>::value>
+    {
+    };
+
+    template <class From>
+    struct is_allowed_element_type_conversion<From, byte>
+        : public std::integral_constant<bool, !std::is_const<From>::value>
+    {
+    };
+
+    template <class From>
+    struct is_allowed_element_type_conversion<From, const byte> : public std::true_type
+    {
+    };
+
+    template <class Span>
+    class const_span_iterator
+    {
+    public:
+        using iterator_category = std::random_access_iterator_tag;
+        using value_type = typename Span::element_type;
+        using difference_type = std::ptrdiff_t;
+
+        using const_pointer = std::add_const_t<value_type*>;
+        using pointer = const_pointer;
+
+        using const_reference = std::add_const_t<value_type&>;
+        using reference = const_reference;
+
+        constexpr const_span_iterator() : const_span_iterator(nullptr, 0) {}
+        constexpr const_span_iterator(const Span* span, typename Span::index_type index)
+            : span_(span), index_(index)
+        {
+            Expects(span == nullptr || (index_ >= 0 && index <= span_->length()));
+        }
+
+        constexpr reference operator*() const
+        {
+            Expects(span_);
+            return (*span_)[index_];
+        }
+
+        constexpr pointer operator->() const
+        {
+            Expects(span_);
+            return &((*span_)[index_]);
+        }
+
+        constexpr const_span_iterator& operator++() noexcept
+        {
+            Expects(span_ && index_ >= 0 && index_ < span_->length());
+            ++index_;
+            return *this;
+        }
+
+        constexpr const_span_iterator operator++(int) noexcept
+        {
+            auto ret = *this;
+            ++(*this);
+            return ret;
+        }
+
+        constexpr const_span_iterator& operator--() noexcept
+        {
+            Expects(span_ && index_ > 0 && index_ <= span_->length());
+            --index_;
+            return *this;
+        }
+
+        constexpr const_span_iterator operator--(int) noexcept
+        {
+            auto ret = *this;
+            --(*this);
+            return ret;
+        }
+
+        constexpr const_span_iterator operator+(difference_type n) const noexcept
+        {
+            auto ret = *this;
+            return ret += n;
+        }
+
+        constexpr const_span_iterator& operator+=(difference_type n) noexcept
+        {
+            Expects(span_ && (index_ + n) >= 0 && (index_ + n) <= span_->length());
+            index_ += n;
+            return *this;
+        }
+
+        constexpr const_span_iterator operator-(difference_type n) const noexcept
+        {
+            auto ret = *this;
+            return ret -= n;
+        }
+
+        constexpr const_span_iterator& operator-=(difference_type n) noexcept
+        {
+            return *this += -n;
+        }
+
+        constexpr difference_type operator-(const const_span_iterator& rhs) const noexcept
+        {
+            Expects(span_ == rhs.span_);
+            return index_ - rhs.index_;
+        }
+
+        constexpr reference operator[](difference_type n) const noexcept { return *(*this + n); }
+
+        constexpr bool operator==(const const_span_iterator& rhs) const noexcept
+        {
+            return span_ == rhs.span_ && index_ == rhs.index_;
+        }
+
+        constexpr bool operator!=(const const_span_iterator& rhs) const noexcept
+        {
+            return !(*this == rhs);
+        }
+
+        constexpr bool operator<(const const_span_iterator& rhs) const noexcept
+        {
+            Expects(span_ == rhs.span_);
+            return index_ < rhs.index_;
+        }
+
+        constexpr bool operator<=(const const_span_iterator& rhs) const noexcept
+        {
+            return !(rhs < *this);
+        }
+
+        constexpr bool operator>(const const_span_iterator& rhs) const noexcept
+        {
+            return rhs < *this;
+        }
+
+        constexpr bool operator>=(const const_span_iterator& rhs) const noexcept
+        {
+            return !(rhs > *this);
+        }
+
+        void swap(const_span_iterator& rhs) noexcept
+        {
+            std::swap(index_, rhs.index_);
+            std::swap(span_, rhs.span_);
+        }
+
+    private:
+        const Span* span_;
+        std::ptrdiff_t index_;
+    };
+
+    template <class Span>
+    class span_iterator
+    {
+    public:
+        using iterator_category = std::random_access_iterator_tag;
+        using value_type = typename Span::element_type;
+        using difference_type = std::ptrdiff_t;
+
+        using pointer = value_type*;
+        using reference = value_type&;
+
+        constexpr span_iterator() : span_iterator(nullptr, 0) {}
+        constexpr span_iterator(const Span* span, typename Span::index_type index)
+            : span_(span), index_(index)
+        {
+            Expects(span == nullptr || (index_ >= 0 && index <= span_->length()));
+        }
+
+        constexpr reference operator*() const
+        {
+            Expects(span_);
+            return (*span_)[index_];
+        }
+
+        constexpr pointer operator->() const
+        {
+            Expects(span_);
+            return &((*span_)[index_]);
+        }
+
+        constexpr span_iterator& operator++() noexcept
+        {
+            Expects(span_ && index_ >= 0 && index_ < span_->length());
+            ++index_;
+            return *this;
+        }
+
+        constexpr span_iterator operator++(int) noexcept
+        {
+            auto ret = *this;
+            ++(*this);
+            return ret;
+        }
+
+        constexpr span_iterator& operator--() noexcept
+        {
+            Expects(span_ && index_ > 0 && index_ <= span_->length());
+            --index_;
+            return *this;
+        }
+
+        constexpr span_iterator operator--(int) noexcept
+        {
+            auto ret = *this;
+            --(*this);
+            return ret;
+        }
+
+        constexpr span_iterator operator+(difference_type n) const noexcept
+        {
+            auto ret = *this;
+            return ret += n;
+        }
+
+        constexpr span_iterator& operator+=(difference_type n) noexcept
+        {
+            Expects(span_ && (index_ + n) >= 0 && (index_ + n) <= span_->length());
+            index_ += n;
+            return *this;
+        }
+
+        constexpr span_iterator operator-(difference_type n) const noexcept
+        {
+            auto ret = *this;
+            return ret -= n;
+        }
+
+        constexpr span_iterator& operator-=(difference_type n) noexcept { return *this += -n; }
+
+        constexpr difference_type operator-(const span_iterator& rhs) const noexcept
+        {
+            Expects(span_ == rhs.span_);
+            return index_ - rhs.index_;
+        }
+
+        constexpr reference operator[](difference_type n) const noexcept { return *(*this + n); }
+
+        constexpr bool operator==(const span_iterator& rhs) const noexcept
+        {
+            return span_ == rhs.span_ && index_ == rhs.index_;
+        }
+
+        constexpr bool operator!=(const span_iterator& rhs) const noexcept
+        {
+            return !(*this == rhs);
+        }
+
+        constexpr bool operator<(const span_iterator& rhs) const noexcept
+        {
+            Expects(span_ == rhs.span_);
+            return index_ < rhs.index_;
+        }
+
+        constexpr bool operator<=(const span_iterator& rhs) const noexcept
+        {
+            return !(rhs < *this);
+        }
+
+        constexpr bool operator>(const span_iterator& rhs) const noexcept { return rhs < *this; }
+
+        constexpr bool operator>=(const span_iterator& rhs) const noexcept
+        {
+            return !(rhs > *this);
+        }
+
+        void swap(span_iterator& rhs) noexcept
+        {
+            std::swap(index_, rhs.index_);
+            std::swap(span_, rhs.span_);
+        }
+
+    private:
+        const Span* span_;
+        std::ptrdiff_t index_;
+    };
+
+    template <typename Span>
+    constexpr const_span_iterator<Span>
+    operator+(typename const_span_iterator<Span>::difference_type n,
+              const const_span_iterator<Span>& rhs) noexcept
+    {
+        return rhs + n;
+    }
+
+    template <typename Span>
+    constexpr const_span_iterator<Span>
+    operator-(typename const_span_iterator<Span>::difference_type n,
+              const const_span_iterator<Span>& rhs) noexcept
+    {
+        return rhs - n;
+    }
+
+    template <typename Span>
+    constexpr span_iterator<Span> operator+(typename span_iterator<Span>::difference_type n,
+                                            const span_iterator<Span>& rhs) noexcept
+    {
+        return rhs + n;
+    }
+
+    template <typename Span>
+    constexpr span_iterator<Span> operator-(typename span_iterator<Span>::difference_type n,
+                                            const span_iterator<Span>& rhs) noexcept
+    {
+        return rhs - n;
+    }
+
+    template <std::ptrdiff_t Ext>
+    class extent_type
+    {
+    public:
+        using index_type = std::ptrdiff_t;
+
+        static_assert(Ext >= 0, "A fixed-size span must be >= 0 in size.");
+
+        constexpr extent_type() noexcept {}
+
+        template <index_type Other>
+        constexpr extent_type(extent_type<Other> ext) noexcept
+        {
+            static_assert(Other == Ext || Other == dynamic_extent,
+                          "Mismatch between fixed-size extent and size of initializing data.");
+            Expects(ext.size() == Ext);
+        }
+
+        constexpr extent_type(index_type size) { Expects(size == Ext); }
+
+        constexpr inline index_type size() const noexcept { return Ext; }
+    };
+
+    template <>
+    class extent_type<dynamic_extent>
+    {
+    public:
+        using index_type = std::ptrdiff_t;
+
+        template <index_type Other>
+        explicit constexpr extent_type(extent_type<Other> ext) : size_(ext.size())
+        {
+        }
+
+        explicit constexpr extent_type(index_type size) : size_(size) { Expects(size >= 0); }
+
+        constexpr inline index_type size() const noexcept { return size_; }
+
+    private:
+        index_type size_;
+    };
+} // namespace details
+
+// [span], class template span
+template <class ElementType, std::ptrdiff_t Extent>
 class span
 {
-    // TODO do we still need this?
-    template <typename ValueType2, std::ptrdiff_t FirstDimension2,
-              std::ptrdiff_t... RestDimensions2>
-    friend class span;
-
 public:
-    using bounds_type = static_bounds<FirstDimension, RestDimensions...>;
-    static const size_t Rank = bounds_type::rank;
-    using size_type = typename bounds_type::size_type;
-    using index_type = typename bounds_type::index_type;
-    using value_type = ValueType;
-    using const_value_type = std::add_const_t<value_type>;
-    using pointer = std::add_pointer_t<value_type>;
-    using reference = std::add_lvalue_reference_t<value_type>;
-    using iterator = contiguous_span_iterator<span>;
-    using const_span = span<const_value_type, FirstDimension, RestDimensions...>;
-    using const_iterator = contiguous_span_iterator<const_span>;
+    // constants and types
+    using element_type = ElementType;
+    using index_type = std::ptrdiff_t;
+    using pointer = element_type*;
+    using reference = element_type&;
+
+    using iterator = details::span_iterator<span<ElementType, Extent>>;
+    using const_iterator = details::const_span_iterator<span<ElementType, Extent>>;
     using reverse_iterator = std::reverse_iterator<iterator>;
     using const_reverse_iterator = std::reverse_iterator<const_iterator>;
-    using sliced_type =
-        std::conditional_t<Rank == 1, value_type, span<value_type, RestDimensions...>>;
+
+    constexpr static const index_type extent = Extent;
+
+    // [span.cons], span constructors, copy, assignment, and destructor
+    constexpr span() noexcept : storage_(nullptr, details::extent_type<0>()) {}
+
+    constexpr span(std::nullptr_t) noexcept : span() {}
+
+    constexpr span(pointer ptr, index_type count) : storage_(ptr, count) {}
+
+    constexpr span(pointer firstElem, pointer lastElem)
+        : storage_(firstElem, std::distance(firstElem, lastElem))
+    {
+    }
+
+    template <size_t N>
+    constexpr span(element_type (&arr)[N]) noexcept : storage_(&arr[0], details::extent_type<N>())
+    {
+    }
+
+    template <size_t N, class ArrayElementType = std::remove_const_t<element_type>>
+    constexpr span(std::array<ArrayElementType, N>& arr) noexcept
+        : storage_(&arr[0], details::extent_type<N>())
+    {
+    }
+
+    template <size_t N>
+    constexpr span(const std::array<std::remove_const_t<element_type>, N>& arr) noexcept
+        : storage_(&arr[0], details::extent_type<N>())
+    {
+    }
+
+    // NB: the SFINAE here uses .data() as a incomplete/imperfect proxy for the requirement
+    // on Container to be a contiguous sequence container.
+    template <class Container,
+              class = std::enable_if_t<
+                  !details::is_span<Container>::value && !details::is_std_array<Container>::value &&
+                  std::is_convertible<typename Container::pointer, pointer>::value &&
+                  std::is_convertible<typename Container::pointer,
+                                      decltype(std::declval<Container>().data())>::value>>
+    constexpr span(Container& cont) : span(cont.data(), cont.size())
+    {
+    }
+
+    template <class Container,
+              class = std::enable_if_t<
+                  std::is_const<element_type>::value && !details::is_span<Container>::value &&
+                  std::is_convertible<typename Container::pointer, pointer>::value &&
+                  std::is_convertible<typename Container::pointer,
+                                      decltype(std::declval<Container>().data())>::value>>
+    constexpr span(const Container& cont) : span(cont.data(), cont.size())
+    {
+    }
+
+    constexpr span(const span& other) noexcept = default;
+#ifndef GSL_MSVC_NO_DEFAULT_MOVE_CTOR
+    constexpr span(span&& other) noexcept = default;
+#else
+    constexpr span(span&& other) noexcept : storage_(std::move(other.storage_)) {}
+#endif
+
+    template <
+        class OtherElementType, std::ptrdiff_t OtherExtent,
+        class = std::enable_if_t<
+            details::is_allowed_extent_conversion<OtherExtent, Extent>::value &&
+            details::is_allowed_element_type_conversion<OtherElementType, element_type>::value>>
+    constexpr span(const span<OtherElementType, OtherExtent>& other)
+        : storage_(reinterpret_cast<pointer>(other.data()),
+                   details::extent_type<OtherExtent>(other.size()))
+    {
+    }
+
+    template <
+        class OtherElementType, std::ptrdiff_t OtherExtent,
+        class = std::enable_if_t<
+            details::is_allowed_extent_conversion<OtherExtent, Extent>::value &&
+            details::is_allowed_element_type_conversion<OtherElementType, element_type>::value>>
+    constexpr span(span<OtherElementType, OtherExtent>&& other)
+        : storage_(reinterpret_cast<pointer>(other.data()),
+                   details::extent_type<OtherExtent>(other.size()))
+    {
+    }
+
+    ~span() noexcept = default;
+    constexpr span& operator=(const span& other) noexcept = default;
+
+#ifndef GSL_MSVC_NO_DEFAULT_MOVE_CTOR
+    constexpr span& operator=(span&& other) noexcept = default;
+#else
+    constexpr span& operator=(span&& other) noexcept
+    {
+        storage_ = std::move(other.storage_);
+        return *this;
+    }
+#endif
+    // [span.sub], span subviews
+    template <std::ptrdiff_t Count>
+    constexpr span<element_type, Count> first() const
+    {
+        Expects(Count >= 0 && Count <= size());
+        return {data(), Count};
+    }
+
+    template <std::ptrdiff_t Count>
+    constexpr span<element_type, Count> last() const
+    {
+        Expects(Count >= 0 && Count <= size());
+        return {data() + (size() - Count), Count};
+    }
+
+    template <std::ptrdiff_t Offset, std::ptrdiff_t Count = dynamic_extent>
+    constexpr span<element_type, Count> subspan() const
+    {
+        Expects((Offset == 0 || (Offset > 0 && Offset <= size())) &&
+                (Count == dynamic_extent || (Count >= 0 && Offset + Count <= size())));
+        return {data() + Offset, Count == dynamic_extent ? size() - Offset : Count};
+    }
+
+    constexpr span<element_type, dynamic_extent> first(index_type count) const
+    {
+        Expects(count >= 0 && count <= size());
+        return {data(), count};
+    }
+
+    constexpr span<element_type, dynamic_extent> last(index_type count) const
+    {
+        Expects(count >= 0 && count <= size());
+        return {data() + (size() - count), count};
+    }
+
+    constexpr span<element_type, dynamic_extent> subspan(index_type offset,
+                                                         index_type count = dynamic_extent) const
+    {
+        Expects((offset == 0 || (offset > 0 && offset <= size())) &&
+                (count == dynamic_extent || (count >= 0 && offset + count <= size())));
+        return {data() + offset, count == dynamic_extent ? size() - offset : count};
+    }
+
+    // [span.obs], span observers
+    constexpr index_type length() const noexcept { return size(); }
+    constexpr index_type size() const noexcept { return storage_.size(); }
+    constexpr index_type length_bytes() const noexcept { return size_bytes(); }
+    constexpr index_type size_bytes() const noexcept { return size() * sizeof(element_type); }
+    constexpr bool empty() const noexcept { return size() == 0; }
+
+    // [span.elem], span element access
+    constexpr reference operator[](index_type idx) const
+    {
+        Expects(idx >= 0 && idx < storage_.size());
+        return data()[idx];
+    }
+    constexpr reference operator()(index_type idx) const { return this->operator[](idx); }
+    constexpr pointer data() const noexcept { return storage_.data(); }
+
+    // [span.iter], span iterator support
+    iterator begin() const noexcept { return {this, 0}; }
+    iterator end() const noexcept { return {this, length()}; }
+
+    const_iterator cbegin() const noexcept { return {this, 0}; }
+    const_iterator cend() const noexcept { return {this, length()}; }
+
+    reverse_iterator rbegin() const noexcept { return reverse_iterator{end()}; }
+    reverse_iterator rend() const noexcept { return reverse_iterator{begin()}; }
+
+    const_reverse_iterator crbegin() const noexcept { return const_reverse_iterator{cend()}; }
+    const_reverse_iterator crend() const noexcept { return const_reverse_iterator{cbegin()}; }
 
 private:
-    pointer data_;
-    bounds_type bounds_;
-
-    friend iterator;
-    friend const_iterator;
-
-public:
-    // default constructor - same as constructing from nullptr_t
-    constexpr span() noexcept : span(nullptr, bounds_type{})
+    // this implementation detail class lets us take advantage of the
+    // empty base class optimization to pay for only storage of a single
+    // pointer in the case of fixed-size spans
+    template <class ExtentType>
+    class storage_type : public ExtentType
     {
-        static_assert(bounds_type::dynamic_rank != 0 ||
-                          (bounds_type::dynamic_rank == 0 && bounds_type::static_size == 0),
-                      "Default construction of span<T> only possible "
-                      "for dynamic or fixed, zero-length spans.");
-    }
+    public:
+        template <class OtherExtentType>
+        constexpr storage_type(pointer data, OtherExtentType ext) : ExtentType(ext), data_(data)
+        {
+            Expects((!data && ExtentType::size() == 0) || (data && ExtentType::size() >= 0));
+        }
 
-    // construct from nullptr - get an empty span
-    constexpr span(std::nullptr_t) noexcept : span(nullptr, bounds_type{})
-    {
-        static_assert(bounds_type::dynamic_rank != 0 ||
-                          (bounds_type::dynamic_rank == 0 && bounds_type::static_size == 0),
-                      "nullptr_t construction of span<T> only possible "
-                      "for dynamic or fixed, zero-length spans.");
-    }
+        constexpr inline pointer data() const noexcept { return data_; }
 
-    // construct from nullptr with size of 0 (helps with template function calls)
-    template <class IntType, typename = std::enable_if_t<std::is_integral<IntType>::value>>
-    constexpr span(std::nullptr_t, IntType size) noexcept : span(nullptr, bounds_type{})
-    {
-        static_assert(bounds_type::dynamic_rank != 0 ||
-                          (bounds_type::dynamic_rank == 0 && bounds_type::static_size == 0),
-                      "nullptr_t construction of span<T> only possible "
-                      "for dynamic or fixed, zero-length spans.");
-        Expects(size == 0);
-    }
+    private:
+        pointer data_;
+    };
 
-    // construct from a single element
-    constexpr span(reference data) noexcept : span(&data, bounds_type{1})
-    {
-        static_assert(bounds_type::dynamic_rank > 0 || bounds_type::static_size == 0 ||
-                          bounds_type::static_size == 1,
-                      "Construction from a single element only possible "
-                      "for dynamic or fixed spans of length 0 or 1.");
-    }
-
-    // prevent constructing from temporaries for single-elements
-    constexpr span(value_type&&) = delete;
-
-    // construct from pointer + length
-    constexpr span(pointer ptr, size_type size) noexcept : span(ptr, bounds_type{size}) {}
-
-    // construct from pointer + length - multidimensional
-    constexpr span(pointer data, bounds_type bounds) noexcept : data_(data),
-                                                                bounds_(std::move(bounds))
-    {
-        Expects((bounds_.size() > 0 && data != nullptr) || bounds_.size() == 0);
-    }
-
-    // construct from begin,end pointer pair
-    template <typename Ptr,
-              typename = std::enable_if_t<std::is_convertible<Ptr, pointer>::value &&
-                                          details::LessThan<bounds_type::dynamic_rank, 2>::value>>
-    constexpr span(pointer begin, Ptr end)
-        : span(begin, details::newBoundsHelper<bounds_type>(static_cast<pointer>(end) - begin))
-    {
-        Expects(begin != nullptr && end != nullptr && begin <= static_cast<pointer>(end));
-    }
-
-    // construct from n-dimensions static array
-    template <typename T, size_t N, typename Helper = details::SpanArrayTraits<T, N>>
-    constexpr span(T (&arr)[N])
-        : span(reinterpret_cast<pointer>(arr), bounds_type{typename Helper::bounds_type{}})
-    {
-        static_assert(
-            std::is_convertible<typename Helper::value_type(*) [], value_type(*) []>::value,
-            "Cannot convert from source type to target span type.");
-        static_assert(std::is_convertible<typename Helper::bounds_type, bounds_type>::value,
-                      "Cannot construct a span from an array with fewer elements.");
-    }
-
-    // construct from n-dimensions dynamic array (e.g. new int[m][4])
-    // (precedence will be lower than the 1-dimension pointer)
-    template <typename T, typename Helper = details::SpanArrayTraits<T, dynamic_range>>
-    constexpr span(T* const& data, size_type size)
-        : span(reinterpret_cast<pointer>(data), typename Helper::bounds_type{size})
-    {
-        static_assert(
-            std::is_convertible<typename Helper::value_type(*) [], value_type(*) []>::value,
-            "Cannot convert from source type to target span type.");
-    }
-
-    // construct from std::array
-    template <typename T, size_t N>
-    constexpr span(std::array<T, N>& arr) : span(arr.data(), bounds_type{static_bounds<N>{}})
-    {
-        static_assert(
-            std::is_convertible<T(*) [], typename std::remove_const_t<value_type>(*) []>::value,
-            "Cannot convert from source type to target span type.");
-        static_assert(std::is_convertible<static_bounds<N>, bounds_type>::value,
-                      "You cannot construct a span from a std::array of smaller size.");
-    }
-
-    // construct from const std::array
-    template <typename T, size_t N>
-    constexpr span(const std::array<std::remove_const_t<value_type>, N>& arr)
-        : span(arr.data(), static_bounds<N>())
-    {
-        static_assert(std::is_convertible<T(*) [], std::remove_const_t<value_type>>::value,
-                      "Cannot convert from source type to target span type.");
-        static_assert(std::is_convertible<static_bounds<N>, bounds_type>::value,
-                      "You cannot construct a span from a std::array of smaller size.");
-    }
-
-    // prevent constructing from temporary std::array
-    template <typename T, size_t N>
-    constexpr span(std::array<T, N>&& arr) = delete;
-
-    // construct from containers
-    // future: could use contiguous_iterator_traits to identify only contiguous containers
-    // type-requirements: container must have .size(), operator[] which are value_type compatible
-    template <typename Cont, typename DataType = typename Cont::value_type,
-              typename = std::enable_if_t<
-                  !details::is_span<Cont>::value &&
-                  std::is_convertible<DataType (*)[], value_type (*)[]>::value &&
-                  std::is_same<std::decay_t<decltype(std::declval<Cont>().size(),
-                                                     *std::declval<Cont>().data())>,
-                               DataType>::value>>
-    constexpr span(Cont& cont)
-        : span(static_cast<pointer>(cont.data()),
-               details::newBoundsHelper<bounds_type>(narrow_cast<size_type>(cont.size())))
-    {
-    }
-
-    // prevent constructing from temporary containers
-    template <typename Cont, typename DataType = typename Cont::value_type,
-              typename = std::enable_if_t<
-                  !details::is_span<Cont>::value &&
-                  std::is_convertible<DataType (*)[], value_type (*)[]>::value &&
-                  std::is_same<std::decay_t<decltype(std::declval<Cont>().size(),
-                                                     *std::declval<Cont>().data())>,
-                               DataType>::value>>
-    explicit constexpr span(Cont&& cont) = delete;
-
-    // construct from a convertible span
-    template <typename OtherValueType, std::ptrdiff_t... OtherDimensions,
-              typename OtherBounds = static_bounds<OtherDimensions...>,
-              typename = std::enable_if_t<std::is_convertible<OtherValueType, ValueType>::value &&
-                                          std::is_convertible<OtherBounds, bounds_type>::value>>
-    constexpr span(span<OtherValueType, OtherDimensions...> other) noexcept : data_(other.data_),
-                                                                              bounds_(other.bounds_)
-    {
-    }
-
-// trivial copy and move
-#ifndef GSL_MSVC_NO_SUPPORT_FOR_MOVE_CTOR_DEFAULT
-    constexpr span(span&&) = default;
-#endif
-    constexpr span(const span&) = default;
-
-// trivial assignment
-#ifndef GSL_MSVC_NO_SUPPORT_FOR_MOVE_CTOR_DEFAULT
-    constexpr span& operator=(span&&) = default;
-#endif
-    constexpr span& operator=(const span&) = default;
-
-    // first() - extract the first Count elements into a new span
-    template <std::ptrdiff_t Count>
-    constexpr span<ValueType, Count> first() const noexcept
-    {
-        static_assert(Count >= 0, "Count must be >= 0.");
-        static_assert(bounds_type::static_size == dynamic_range ||
-                          Count <= bounds_type::static_size,
-                      "Count is out of bounds.");
-
-        Expects(bounds_type::static_size != dynamic_range || Count <= this->size());
-        return {this->data(), Count};
-    }
-
-    // first() - extract the first count elements into a new span
-    constexpr span<ValueType, dynamic_range> first(size_type count) const noexcept
-    {
-        Expects(count >= 0 && count <= this->size());
-        return {this->data(), count};
-    }
-
-    // last() - extract the last Count elements into a new span
-    template <std::ptrdiff_t Count>
-    constexpr span<ValueType, Count> last() const noexcept
-    {
-        static_assert(Count >= 0, "Count must be >= 0.");
-        static_assert(bounds_type::static_size == dynamic_range ||
-                          Count <= bounds_type::static_size,
-                      "Count is out of bounds.");
-
-        Expects(bounds_type::static_size != dynamic_range || Count <= this->size());
-        return {this->data() + this->size() - Count, Count};
-    }
-
-    // last() - extract the last count elements into a new span
-    constexpr span<ValueType, dynamic_range> last(size_type count) const noexcept
-    {
-        Expects(count >= 0 && count <= this->size());
-        return {this->data() + this->size() - count, count};
-    }
-
-    // subspan() - create a subview of Count elements starting at Offset
-    template <std::ptrdiff_t Offset, std::ptrdiff_t Count>
-    constexpr span<ValueType, Count> subspan() const noexcept
-    {
-        static_assert(Count >= 0, "Count must be >= 0.");
-        static_assert(Offset >= 0, "Offset must be >= 0.");
-        static_assert(bounds_type::static_size == dynamic_range ||
-                          ((Offset <= bounds_type::static_size) &&
-                           Count <= bounds_type::static_size - Offset),
-                      "You must describe a sub-range within bounds of the span.");
-
-        Expects(bounds_type::static_size != dynamic_range ||
-                (Offset <= this->size() && Count <= this->size() - Offset));
-        return {this->data() + Offset, Count};
-    }
-
-    // subspan() - create a subview of count elements starting at offset
-    // supplying dynamic_range for count will consume all available elements from offset
-    constexpr span<ValueType, dynamic_range> subspan(size_type offset,
-                                                     size_type count = dynamic_range) const noexcept
-    {
-        Expects((offset >= 0 && offset <= this->size()) &&
-                (count == dynamic_range || (count <= this->size() - offset)));
-        return {this->data() + offset, count == dynamic_range ? this->length() - offset : count};
-    }
-
-    // section - creates a non-contiguous, strided span from a contiguous one
-    constexpr strided_span<ValueType, Rank> section(index_type origin, index_type extents) const
-        noexcept
-    {
-        size_type size = this->bounds().total_size() - this->bounds().linearize(origin);
-        return {&this->operator[](origin), size,
-                strided_bounds<Rank>{extents, details::make_stride(bounds())}};
-    }
-
-    // length of the span in elements
-    constexpr size_type size() const noexcept { return bounds_.size(); }
-
-    // length of the span in elements
-    constexpr size_type length() const noexcept { return this->size(); }
-
-    // length of the span in bytes
-    constexpr size_type size_bytes() const noexcept { return sizeof(value_type) * this->size(); }
-
-    // length of the span in bytes
-    constexpr size_type length_bytes() const noexcept { return this->size_bytes(); }
-
-    constexpr bool empty() const noexcept { return this->size() == 0; }
-
-    static constexpr std::size_t rank() { return Rank; }
-
-    template <size_t Dim = 0>
-    constexpr size_type extent() const noexcept
-    {
-        static_assert(Dim < Rank,
-                      "Dimension should be less than rank (dimension count starts from 0).");
-        return bounds_.template extent<Dim>();
-    }
-
-    template <typename IntType>
-    constexpr size_type extent(IntType dim) const noexcept
-    {
-        return bounds_.extent(dim);
-    }
-
-    constexpr bounds_type bounds() const noexcept { return bounds_; }
-
-    constexpr pointer data() const noexcept { return data_; }
-
-    template <typename FirstIndex>
-    constexpr reference operator()(FirstIndex index)
-    {
-        return this->operator[](narrow_cast<std::ptrdiff_t>(index));
-    }
-
-    template <typename FirstIndex, typename... OtherIndices>
-    constexpr reference operator()(FirstIndex index, OtherIndices... indices)
-    {
-        index_type idx = {narrow_cast<std::ptrdiff_t>(index),
-                          narrow_cast<std::ptrdiff_t>(indices...)};
-        return this->operator[](idx);
-    }
-
-    constexpr reference operator[](const index_type& idx) const noexcept
-    {
-        return data_[bounds_.linearize(idx)];
-    }
-
-    template <bool Enabled = (Rank > 1), typename Ret = std::enable_if_t<Enabled, sliced_type>>
-    constexpr Ret operator[](size_type idx) const noexcept
-    {
-        Expects(idx < bounds_.size()); // index is out of bounds of the array
-        const size_type ridx = idx * bounds_.stride();
-
-        // index is out of bounds of the underlying data
-        Expects(ridx < bounds_.total_size());
-        return Ret{data_ + ridx, bounds_.slice()};
-    }
-
-    constexpr iterator begin() const noexcept { return iterator{this, true}; }
-
-    constexpr iterator end() const noexcept { return iterator{this, false}; }
-
-    constexpr const_iterator cbegin() const noexcept
-    {
-        return const_iterator{reinterpret_cast<const const_span*>(this), true};
-    }
-
-    constexpr const_iterator cend() const noexcept
-    {
-        return const_iterator{reinterpret_cast<const const_span*>(this), false};
-    }
-
-    constexpr reverse_iterator rbegin() const noexcept { return reverse_iterator{end()}; }
-
-    constexpr reverse_iterator rend() const noexcept { return reverse_iterator{begin()}; }
-
-    constexpr const_reverse_iterator crbegin() const noexcept
-    {
-        return const_reverse_iterator{cend()};
-    }
-
-    constexpr const_reverse_iterator crend() const noexcept
-    {
-        return const_reverse_iterator{cbegin()};
-    }
-
-    template <typename OtherValueType, std::ptrdiff_t... OtherDimensions,
-              typename Dummy = std::enable_if_t<std::is_same<
-                  std::remove_cv_t<value_type>, std::remove_cv_t<OtherValueType>>::value>>
-    constexpr bool operator==(const span<OtherValueType, OtherDimensions...>& other) const noexcept
-    {
-        return bounds_.size() == other.bounds_.size() &&
-               (data_ == other.data_ || std::equal(this->begin(), this->end(), other.begin()));
-    }
-
-    template <typename OtherValueType, std::ptrdiff_t... OtherDimensions,
-              typename Dummy = std::enable_if_t<std::is_same<
-                  std::remove_cv_t<value_type>, std::remove_cv_t<OtherValueType>>::value>>
-    constexpr bool operator!=(const span<OtherValueType, OtherDimensions...>& other) const noexcept
-    {
-        return !(*this == other);
-    }
-
-    template <typename OtherValueType, std::ptrdiff_t... OtherDimensions,
-              typename Dummy = std::enable_if_t<std::is_same<
-                  std::remove_cv_t<value_type>, std::remove_cv_t<OtherValueType>>::value>>
-    constexpr bool operator<(const span<OtherValueType, OtherDimensions...>& other) const noexcept
-    {
-        return std::lexicographical_compare(this->begin(), this->end(), other.begin(), other.end());
-    }
-
-    template <typename OtherValueType, std::ptrdiff_t... OtherDimensions,
-              typename Dummy = std::enable_if_t<std::is_same<
-                  std::remove_cv_t<value_type>, std::remove_cv_t<OtherValueType>>::value>>
-    constexpr bool operator<=(const span<OtherValueType, OtherDimensions...>& other) const noexcept
-    {
-        return !(other < *this);
-    }
-
-    template <typename OtherValueType, std::ptrdiff_t... OtherDimensions,
-              typename Dummy = std::enable_if_t<std::is_same<
-                  std::remove_cv_t<value_type>, std::remove_cv_t<OtherValueType>>::value>>
-    constexpr bool operator>(const span<OtherValueType, OtherDimensions...>& other) const noexcept
-    {
-        return (other < *this);
-    }
-
-    template <typename OtherValueType, std::ptrdiff_t... OtherDimensions,
-              typename Dummy = std::enable_if_t<std::is_same<
-                  std::remove_cv_t<value_type>, std::remove_cv_t<OtherValueType>>::value>>
-    constexpr bool operator>=(const span<OtherValueType, OtherDimensions...>& other) const noexcept
-    {
-        return !(*this < other);
-    }
+    storage_type<details::extent_type<Extent>> storage_;
 };
 
-//
-// Free functions for manipulating spans
-//
-
-// reshape a span into a different dimensionality
-// DimCount and Enabled here are workarounds for a bug in MSVC 2015
-template <typename SpanType, typename... Dimensions2, size_t DimCount = sizeof...(Dimensions2),
-          bool Enabled = (DimCount > 0), typename = std::enable_if_t<Enabled>>
-constexpr span<typename SpanType::value_type, Dimensions2::value...> as_span(SpanType s,
-                                                                             Dimensions2... dims)
+// [span.comparison], span comparison operators
+template <class ElementType, std::ptrdiff_t FirstExtent, std::ptrdiff_t SecondExtent>
+constexpr bool operator==(const span<ElementType, FirstExtent>& l,
+                          const span<ElementType, SecondExtent>& r)
 {
-    static_assert(details::is_span<SpanType>::value,
-                  "Variadic as_span() is for reshaping existing spans.");
-    using BoundsType =
-        typename span<typename SpanType::value_type, (Dimensions2::value)...>::bounds_type;
-    auto tobounds = details::static_as_span_helper<BoundsType>(dims..., details::Sep{});
-    details::verifyBoundsReshape(s.bounds(), tobounds);
-    return {s.data(), tobounds};
+#ifdef GSL_MSVC_NO_CPP14_STD_EQUAL
+    return (l.size() == r.size()) && std::equal(l.begin(), l.end(), r.begin());
+#else
+    return std::equal(l.begin(), l.end(), r.begin(), r.end());
+#endif
 }
 
-// convert a span<T> to a span<const byte>
-template <typename U, std::ptrdiff_t... Dimensions>
-span<const byte, dynamic_range> as_bytes(span<U, Dimensions...> s) noexcept
+template <class ElementType, std::ptrdiff_t Extent>
+constexpr bool operator!=(const span<ElementType, Extent>& l, const span<ElementType, Extent>& r)
+{
+    return !(l == r);
+}
+
+template <class ElementType, std::ptrdiff_t Extent>
+constexpr bool operator<(const span<ElementType, Extent>& l, const span<ElementType, Extent>& r)
+{
+    return std::lexicographical_compare(l.begin(), l.end(), r.begin(), r.end());
+}
+
+template <class ElementType, std::ptrdiff_t Extent>
+constexpr bool operator<=(const span<ElementType, Extent>& l, const span<ElementType, Extent>& r)
+{
+    return !(l > r);
+}
+
+template <class ElementType, std::ptrdiff_t Extent>
+constexpr bool operator>(const span<ElementType, Extent>& l, const span<ElementType, Extent>& r)
+{
+    return r < l;
+}
+
+template <class ElementType, std::ptrdiff_t Extent>
+constexpr bool operator>=(const span<ElementType, Extent>& l, const span<ElementType, Extent>& r)
+{
+    return !(l < r);
+}
+
+namespace details
+{
+    // if we only supported compilers with good constexpr support then
+    // this pair of classes could collapse down to a constexpr function
+
+    // we should use a narrow_cast<> to go to size_t, but older compilers may not see it as
+    // constexpr
+    // and so will fail compilation of the template
+    template <class ElementType, std::ptrdiff_t Extent>
+    struct calculate_byte_size
+        : std::integral_constant<std::ptrdiff_t,
+                                 static_cast<std::ptrdiff_t>(sizeof(ElementType) *
+                                                             static_cast<std::size_t>(Extent))>
+    {
+    };
+
+    template <class ElementType>
+    struct calculate_byte_size<ElementType, dynamic_extent>
+        : std::integral_constant<std::ptrdiff_t, dynamic_extent>
+    {
+    };
+}
+
+// [span.objectrep], views of object representation
+template <class ElementType, std::ptrdiff_t Extent>
+span<const byte, details::calculate_byte_size<ElementType, Extent>::value>
+as_bytes(span<ElementType, Extent> s) noexcept
 {
-    static_assert(std::is_trivial<std::decay_t<U>>::value,
-                  "The value_type of span must be a trivial type.");
     return {reinterpret_cast<const byte*>(s.data()), s.size_bytes()};
 }
 
-// convert a span<T> to a span<byte> (a writeable byte span)
-// this is not currently a portable function that can be relied upon to work
-// on all implementations. It should be considered an experimental extension
-// to the standard GSL interface.
-template <typename U, std::ptrdiff_t... Dimensions>
-span<byte> as_writeable_bytes(span<U, Dimensions...> s) noexcept
+template <class ElementType, std::ptrdiff_t Extent,
+          class = std::enable_if_t<!std::is_const<ElementType>::value>>
+span<byte, details::calculate_byte_size<ElementType, Extent>::value>
+as_writeable_bytes(span<ElementType, Extent> s) noexcept
 {
-    static_assert(std::is_trivial<std::decay_t<U>>::value,
-                  "The value_type of span must be a trivial type.");
     return {reinterpret_cast<byte*>(s.data()), s.size_bytes()};
 }
 
-// convert a span<const byte> to a span<const T>
-// this is not currently a portable function that can be relied upon to work
-// on all implementations. It should be considered an experimental extension
-// to the standard GSL interface.
-template <typename U, std::ptrdiff_t... Dimensions>
-constexpr auto as_span(span<const byte, Dimensions...> s) noexcept
-    -> span<const U, static_cast<std::ptrdiff_t>(
-                         span<const byte, Dimensions...>::bounds_type::static_size != dynamic_range
-                             ? (static_cast<size_t>(
-                                    span<const byte, Dimensions...>::bounds_type::static_size) /
-                                sizeof(U))
-                             : dynamic_range)>
-{
-    using ConstByteSpan = span<const byte, Dimensions...>;
-    static_assert(
-        std::is_trivial<std::decay_t<U>>::value &&
-            (ConstByteSpan::bounds_type::static_size == dynamic_range ||
-             ConstByteSpan::bounds_type::static_size % narrow_cast<std::ptrdiff_t>(sizeof(U)) == 0),
-        "Target type must be a trivial type and its size must match the byte array size");
-
-    Expects((s.size_bytes() % sizeof(U)) == 0 && (s.size_bytes() / sizeof(U)) < PTRDIFF_MAX);
-    return {reinterpret_cast<const U*>(s.data()),
-            s.size_bytes() / narrow_cast<std::ptrdiff_t>(sizeof(U))};
-}
-
-// convert a span<byte> to a span<T>
-// this is not currently a portable function that can be relied upon to work
-// on all implementations. It should be considered an experimental extension
-// to the standard GSL interface.
-template <typename U, std::ptrdiff_t... Dimensions>
-constexpr auto as_span(span<byte, Dimensions...> s) noexcept -> span<
-    U, narrow_cast<std::ptrdiff_t>(
-           span<byte, Dimensions...>::bounds_type::static_size != dynamic_range
-               ? static_cast<std::size_t>(span<byte, Dimensions...>::bounds_type::static_size) /
-                     sizeof(U)
-               : dynamic_range)>
-{
-    using ByteSpan = span<byte, Dimensions...>;
-    static_assert(
-        std::is_trivial<std::decay_t<U>>::value &&
-            (ByteSpan::bounds_type::static_size == dynamic_range ||
-             ByteSpan::bounds_type::static_size % static_cast<std::size_t>(sizeof(U)) == 0),
-        "Target type must be a trivial type and its size must match the byte array size");
-
-    Expects((s.size_bytes() % sizeof(U)) == 0);
-    return {reinterpret_cast<U*>(s.data()),
-            s.size_bytes() / narrow_cast<std::ptrdiff_t>(sizeof(U))};
-}
-
-template <typename T, std::ptrdiff_t... Dimensions>
-constexpr auto as_span(T* const& ptr, dim<Dimensions>... args)
-    -> span<std::remove_all_extents_t<T>, Dimensions...>
-{
-    return {reinterpret_cast<std::remove_all_extents_t<T>*>(ptr),
-            details::static_as_span_helper<static_bounds<Dimensions...>>(args..., details::Sep{})};
-}
-
-template <typename T>
-constexpr auto as_span(T* arr, std::ptrdiff_t len) ->
-    typename details::SpanArrayTraits<T, dynamic_range>::type
-{
-    return {reinterpret_cast<std::remove_all_extents_t<T>*>(arr), len};
-}
-
-template <typename T, size_t N>
-constexpr auto as_span(T (&arr)[N]) -> typename details::SpanArrayTraits<T, N>::type
-{
-    return {arr};
-}
-
-template <typename T, size_t N>
-constexpr span<const T, N> as_span(const std::array<T, N>& arr)
-{
-    return {arr};
-}
-
-template <typename T, size_t N>
-constexpr span<const T, N> as_span(const std::array<T, N>&&) = delete;
-
-template <typename T, size_t N>
-constexpr span<T, N> as_span(std::array<T, N>& arr)
-{
-    return {arr};
-}
-
-template <typename T>
-constexpr span<T, dynamic_range> as_span(T* begin, T* end)
-{
-    return {begin, end};
-}
-
-template <typename Cont>
-constexpr auto as_span(Cont& arr) -> std::enable_if_t<
-    !details::is_span<std::decay_t<Cont>>::value,
-    span<std::remove_reference_t<decltype(arr.size(), *arr.data())>, dynamic_range>>
-{
-    Expects(arr.size() < PTRDIFF_MAX);
-    return {arr.data(), narrow_cast<std::ptrdiff_t>(arr.size())};
-}
-
-template <typename Cont>
-constexpr auto as_span(Cont&& arr) -> std::enable_if_t<
-    !details::is_span<std::decay_t<Cont>>::value,
-    span<std::remove_reference_t<decltype(arr.size(), *arr.data())>, dynamic_range>> = delete;
-
-// from basic_string which doesn't have nonconst .data() member like other contiguous containers
-template <typename CharT, typename Traits, typename Allocator>
-constexpr auto as_span(std::basic_string<CharT, Traits, Allocator>& str)
-    -> span<CharT, dynamic_range>
-{
-    Expects(str.size() < PTRDIFF_MAX);
-    return {&str[0], narrow_cast<std::ptrdiff_t>(str.size())};
-}
-
-// strided_span is an extension that is not strictly part of the GSL at this time.
-// It is kept here while the multidimensional interface is still being defined.
-template <typename ValueType, size_t Rank>
-class strided_span
-{
-public:
-    using bounds_type = strided_bounds<Rank>;
-    using size_type = typename bounds_type::size_type;
-    using index_type = typename bounds_type::index_type;
-    using value_type = ValueType;
-    using const_value_type = std::add_const_t<value_type>;
-    using pointer = std::add_pointer_t<value_type>;
-    using reference = std::add_lvalue_reference_t<value_type>;
-    using iterator = general_span_iterator<strided_span>;
-    using const_strided_span = strided_span<const_value_type, Rank>;
-    using const_iterator = general_span_iterator<const_strided_span>;
-    using reverse_iterator = std::reverse_iterator<iterator>;
-    using const_reverse_iterator = std::reverse_iterator<const_iterator>;
-    using sliced_type =
-        std::conditional_t<Rank == 1, value_type, strided_span<value_type, Rank - 1>>;
-
-private:
-    pointer data_;
-    bounds_type bounds_;
-
-    friend iterator;
-    friend const_iterator;
-    template <typename OtherValueType, size_t OtherRank>
-    friend class strided_span;
-
-public:
-    // from raw data
-    constexpr strided_span(pointer ptr, size_type size, bounds_type bounds)
-        : data_(ptr), bounds_(std::move(bounds))
-    {
-        Expects((bounds_.size() > 0 && ptr != nullptr) || bounds_.size() == 0);
-        // Bounds cross data boundaries
-        Expects(this->bounds().total_size() <= size);
-        (void) size;
-    }
-
-    // from static array of size N
-    template <size_type N>
-    constexpr strided_span(value_type (&values)[N], bounds_type bounds)
-        : strided_span(values, N, std::move(bounds))
-    {
-    }
-
-    // from array view
-    template <typename OtherValueType, std::ptrdiff_t... Dimensions,
-              bool Enabled1 = (sizeof...(Dimensions) == Rank),
-              bool Enabled2 = std::is_convertible<OtherValueType*, ValueType*>::value,
-              typename Dummy = std::enable_if_t<Enabled1 && Enabled2>>
-    constexpr strided_span(span<OtherValueType, Dimensions...> av, bounds_type bounds)
-        : strided_span(av.data(), av.bounds().total_size(), std::move(bounds))
-    {
-    }
-
-    // convertible
-    template <typename OtherValueType, typename Dummy = std::enable_if_t<std::is_convertible<
-                                           OtherValueType (*)[], value_type (*)[]>::value>>
-    constexpr strided_span(const strided_span<OtherValueType, Rank>& other)
-        : data_(other.data_), bounds_(other.bounds_)
-    {
-    }
-
-    // convert from bytes
-    template <typename OtherValueType>
-    constexpr strided_span<
-        typename std::enable_if<std::is_same<value_type, const byte>::value, OtherValueType>::type,
-        Rank>
-    as_strided_span() const
-    {
-        static_assert((sizeof(OtherValueType) >= sizeof(value_type)) &&
-                          (sizeof(OtherValueType) % sizeof(value_type) == 0),
-                      "OtherValueType should have a size to contain a multiple of ValueTypes");
-        auto d = narrow_cast<size_type>(sizeof(OtherValueType) / sizeof(value_type));
-
-        size_type size = this->bounds().total_size() / d;
-        return {const_cast<OtherValueType*>(reinterpret_cast<const OtherValueType*>(this->data())), size,
-                bounds_type{resize_extent(this->bounds().index_bounds(), d),
-                            resize_stride(this->bounds().strides(), d)}};
-    }
-
-    constexpr strided_span section(index_type origin, index_type extents) const
-    {
-        size_type size = this->bounds().total_size() - this->bounds().linearize(origin);
-        return {&this->operator[](origin), size,
-                bounds_type{extents, details::make_stride(bounds())}};
-    }
-
-    constexpr reference operator[](const index_type& idx) const
-    {
-        return data_[bounds_.linearize(idx)];
-    }
-
-    template <bool Enabled = (Rank > 1), typename Ret = std::enable_if_t<Enabled, sliced_type>>
-    constexpr Ret operator[](size_type idx) const
-    {
-        Expects(idx < bounds_.size()); // index is out of bounds of the array
-        const size_type ridx = idx * bounds_.stride();
-
-        // index is out of bounds of the underlying data
-        Expects(ridx < bounds_.total_size());
-        return {data_ + ridx, bounds_.slice().total_size(), bounds_.slice()};
-    }
-
-    constexpr bounds_type bounds() const noexcept { return bounds_; }
-
-    template <size_t Dim = 0>
-    constexpr size_type extent() const noexcept
-    {
-        static_assert(Dim < Rank,
-                      "dimension should be less than Rank (dimension count starts from 0)");
-        return bounds_.template extent<Dim>();
-    }
-
-    constexpr size_type size() const noexcept { return bounds_.size(); }
-
-    constexpr pointer data() const noexcept { return data_; }
-
-    constexpr explicit operator bool() const noexcept { return data_ != nullptr; }
-
-    constexpr iterator begin() const { return iterator{this, true}; }
-
-    constexpr iterator end() const { return iterator{this, false}; }
-
-    constexpr const_iterator cbegin() const
-    {
-        return const_iterator{reinterpret_cast<const const_strided_span*>(this), true};
-    }
-
-    constexpr const_iterator cend() const
-    {
-        return const_iterator{reinterpret_cast<const const_strided_span*>(this), false};
-    }
-
-    constexpr reverse_iterator rbegin() const { return reverse_iterator{end()}; }
-
-    constexpr reverse_iterator rend() const { return reverse_iterator{begin()}; }
-
-    constexpr const_reverse_iterator crbegin() const { return const_reverse_iterator{cend()}; }
-
-    constexpr const_reverse_iterator crend() const { return const_reverse_iterator{cbegin()}; }
-
-    template <typename OtherValueType, std::ptrdiff_t OtherRank,
-              typename Dummy = std::enable_if_t<std::is_same<
-                  std::remove_cv_t<value_type>, std::remove_cv_t<OtherValueType>>::value>>
-    constexpr bool operator==(const strided_span<OtherValueType, OtherRank>& other) const noexcept
-    {
-        return bounds_.size() == other.bounds_.size() &&
-               (data_ == other.data_ || std::equal(this->begin(), this->end(), other.begin()));
-    }
-
-    template <typename OtherValueType, std::ptrdiff_t OtherRank,
-              typename Dummy = std::enable_if_t<std::is_same<
-                  std::remove_cv_t<value_type>, std::remove_cv_t<OtherValueType>>::value>>
-    constexpr bool operator!=(const strided_span<OtherValueType, OtherRank>& other) const noexcept
-    {
-        return !(*this == other);
-    }
-
-    template <typename OtherValueType, std::ptrdiff_t OtherRank,
-              typename Dummy = std::enable_if_t<std::is_same<
-                  std::remove_cv_t<value_type>, std::remove_cv_t<OtherValueType>>::value>>
-    constexpr bool operator<(const strided_span<OtherValueType, OtherRank>& other) const noexcept
-    {
-        return std::lexicographical_compare(this->begin(), this->end(), other.begin(), other.end());
-    }
-
-    template <typename OtherValueType, std::ptrdiff_t OtherRank,
-              typename Dummy = std::enable_if_t<std::is_same<
-                  std::remove_cv_t<value_type>, std::remove_cv_t<OtherValueType>>::value>>
-    constexpr bool operator<=(const strided_span<OtherValueType, OtherRank>& other) const noexcept
-    {
-        return !(other < *this);
-    }
-
-    template <typename OtherValueType, std::ptrdiff_t OtherRank,
-              typename Dummy = std::enable_if_t<std::is_same<
-                  std::remove_cv_t<value_type>, std::remove_cv_t<OtherValueType>>::value>>
-    constexpr bool operator>(const strided_span<OtherValueType, OtherRank>& other) const noexcept
-    {
-        return (other < *this);
-    }
-
-    template <typename OtherValueType, std::ptrdiff_t OtherRank,
-              typename Dummy = std::enable_if_t<std::is_same<
-                  std::remove_cv_t<value_type>, std::remove_cv_t<OtherValueType>>::value>>
-    constexpr bool operator>=(const strided_span<OtherValueType, OtherRank>& other) const noexcept
-    {
-        return !(*this < other);
-    }
-
-private:
-    static index_type resize_extent(const index_type& extent, std::ptrdiff_t d)
-    {
-        // The last dimension of the array needs to contain a multiple of new type elements
-        Expects(extent[Rank - 1] >= d && (extent[Rank - 1] % d == 0));
-
-        index_type ret = extent;
-        ret[Rank - 1] /= d;
-
-        return ret;
-    }
-
-    template <bool Enabled = (Rank == 1), typename Dummy = std::enable_if_t<Enabled>>
-    static index_type resize_stride(const index_type& strides, std::ptrdiff_t, void* = 0)
-    {
-        // Only strided arrays with regular strides can be resized
-        Expects(strides[Rank - 1] == 1);
-
-        return strides;
-    }
-
-    template <bool Enabled = (Rank > 1), typename Dummy = std::enable_if_t<Enabled>>
-    static index_type resize_stride(const index_type& strides, std::ptrdiff_t d)
-    {
-        // Only strided arrays with regular strides can be resized
-        Expects(strides[Rank - 1] == 1);
-        // The strides must have contiguous chunks of
-        // memory that can contain a multiple of new type elements
-        Expects(strides[Rank - 2] >= d && (strides[Rank - 2] % d == 0));
-
-        for (size_t i = Rank - 1; i > 0; --i) {
-            // Only strided arrays with regular strides can be resized
-            Expects((strides[i - 1] >= strides[i]) && (strides[i - 1] % strides[i] == 0));
-        }
-
-        index_type ret = strides / d;
-        ret[Rank - 1] = 1;
-
-        return ret;
-    }
-};
-
-template <class Span>
-class contiguous_span_iterator
-    : public std::iterator<std::random_access_iterator_tag, typename Span::value_type>
-{
-    using Base = std::iterator<std::random_access_iterator_tag, typename Span::value_type>;
-
-public:
-    using typename Base::reference;
-    using typename Base::pointer;
-    using typename Base::difference_type;
-
-private:
-    template <typename ValueType, std::ptrdiff_t FirstDimension, std::ptrdiff_t... RestDimensions>
-    friend class span;
-
-    pointer data_;
-    const Span* m_validator;
-    void validateThis() const
-    {
-        // iterator is out of range of the array
-        Expects(data_ >= m_validator->data_ && data_ < m_validator->data_ + m_validator->size());
-    }
-    contiguous_span_iterator(const Span* container, bool isbegin)
-        : data_(isbegin ? container->data_ : container->data_ + container->size())
-        , m_validator(container)
-    {
-    }
-
-public:
-    reference operator*() const noexcept
-    {
-        validateThis();
-        return *data_;
-    }
-    pointer operator->() const noexcept
-    {
-        validateThis();
-        return data_;
-    }
-    contiguous_span_iterator& operator++() noexcept
-    {
-        ++data_;
-        return *this;
-    }
-    contiguous_span_iterator operator++(int) noexcept
-    {
-        auto ret = *this;
-        ++(*this);
-        return ret;
-    }
-    contiguous_span_iterator& operator--() noexcept
-    {
-        --data_;
-        return *this;
-    }
-    contiguous_span_iterator operator--(int) noexcept
-    {
-        auto ret = *this;
-        --(*this);
-        return ret;
-    }
-    contiguous_span_iterator operator+(difference_type n) const noexcept
-    {
-        contiguous_span_iterator ret{*this};
-        return ret += n;
-    }
-    contiguous_span_iterator& operator+=(difference_type n) noexcept
-    {
-        data_ += n;
-        return *this;
-    }
-    contiguous_span_iterator operator-(difference_type n) const noexcept
-    {
-        contiguous_span_iterator ret{*this};
-        return ret -= n;
-    }
-    contiguous_span_iterator& operator-=(difference_type n) noexcept { return * this += -n; }
-    difference_type operator-(const contiguous_span_iterator& rhs) const noexcept
-    {
-        Expects(m_validator == rhs.m_validator);
-        return data_ - rhs.data_;
-    }
-    reference operator[](difference_type n) const noexcept { return *(*this + n); }
-    bool operator==(const contiguous_span_iterator& rhs) const noexcept
-    {
-        Expects(m_validator == rhs.m_validator);
-        return data_ == rhs.data_;
-    }
-    bool operator!=(const contiguous_span_iterator& rhs) const noexcept { return !(*this == rhs); }
-    bool operator<(const contiguous_span_iterator& rhs) const noexcept
-    {
-        Expects(m_validator == rhs.m_validator);
-        return data_ < rhs.data_;
-    }
-    bool operator<=(const contiguous_span_iterator& rhs) const noexcept { return !(rhs < *this); }
-    bool operator>(const contiguous_span_iterator& rhs) const noexcept { return rhs < *this; }
-    bool operator>=(const contiguous_span_iterator& rhs) const noexcept { return !(rhs > *this); }
-    void swap(contiguous_span_iterator& rhs) noexcept
-    {
-        std::swap(data_, rhs.data_);
-        std::swap(m_validator, rhs.m_validator);
-    }
-};
-
-template <typename Span>
-contiguous_span_iterator<Span> operator+(typename contiguous_span_iterator<Span>::difference_type n,
-                                         const contiguous_span_iterator<Span>& rhs) noexcept
-{
-    return rhs + n;
-}
-
-template <typename Span>
-class general_span_iterator
-    : public std::iterator<std::random_access_iterator_tag, typename Span::value_type>
-{
-    using Base = std::iterator<std::random_access_iterator_tag, typename Span::value_type>;
-
-public:
-    using typename Base::reference;
-    using typename Base::pointer;
-    using typename Base::difference_type;
-    using typename Base::value_type;
-
-private:
-    template <typename ValueType, size_t Rank>
-    friend class strided_span;
-
-    const Span* m_container;
-    typename Span::bounds_type::iterator m_itr;
-    general_span_iterator(const Span* container, bool isbegin)
-        : m_container(container)
-        , m_itr(isbegin ? m_container->bounds().begin() : m_container->bounds().end())
-    {
-    }
-
-public:
-    reference operator*() noexcept { return (*m_container)[*m_itr]; }
-    pointer operator->() noexcept { return &(*m_container)[*m_itr]; }
-    general_span_iterator& operator++() noexcept
-    {
-        ++m_itr;
-        return *this;
-    }
-    general_span_iterator operator++(int) noexcept
-    {
-        auto ret = *this;
-        ++(*this);
-        return ret;
-    }
-    general_span_iterator& operator--() noexcept
-    {
-        --m_itr;
-        return *this;
-    }
-    general_span_iterator operator--(int) noexcept
-    {
-        auto ret = *this;
-        --(*this);
-        return ret;
-    }
-    general_span_iterator operator+(difference_type n) const noexcept
-    {
-        general_span_iterator ret{*this};
-        return ret += n;
-    }
-    general_span_iterator& operator+=(difference_type n) noexcept
-    {
-        m_itr += n;
-        return *this;
-    }
-    general_span_iterator operator-(difference_type n) const noexcept
-    {
-        general_span_iterator ret{*this};
-        return ret -= n;
-    }
-    general_span_iterator& operator-=(difference_type n) noexcept { return * this += -n; }
-    difference_type operator-(const general_span_iterator& rhs) const noexcept
-    {
-        Expects(m_container == rhs.m_container);
-        return m_itr - rhs.m_itr;
-    }
-    value_type operator[](difference_type n) const noexcept
-    {
-        return (*m_container)[m_itr[n]];
-        ;
-    }
-    bool operator==(const general_span_iterator& rhs) const noexcept
-    {
-        Expects(m_container == rhs.m_container);
-        return m_itr == rhs.m_itr;
-    }
-    bool operator!=(const general_span_iterator& rhs) const noexcept { return !(*this == rhs); }
-    bool operator<(const general_span_iterator& rhs) const noexcept
-    {
-        Expects(m_container == rhs.m_container);
-        return m_itr < rhs.m_itr;
-    }
-    bool operator<=(const general_span_iterator& rhs) const noexcept { return !(rhs < *this); }
-    bool operator>(const general_span_iterator& rhs) const noexcept { return rhs < *this; }
-    bool operator>=(const general_span_iterator& rhs) const noexcept { return !(rhs > *this); }
-    void swap(general_span_iterator& rhs) noexcept
-    {
-        std::swap(m_itr, rhs.m_itr);
-        std::swap(m_container, rhs.m_container);
-    }
-};
-
-template <typename Span>
-general_span_iterator<Span> operator+(typename general_span_iterator<Span>::difference_type n,
-                                      const general_span_iterator<Span>& rhs) noexcept
-{
-    return rhs + n;
-}
-
 } // namespace gsl
 
 #ifdef _MSC_VER
@@ -2210,6 +801,8 @@ general_span_iterator<Span> operator+(typename general_span_iterator<Span>::diff
 #pragma pop_macro("noexcept")
 #endif // GSL_THROW_ON_CONTRACT_VIOLATION
 
+#pragma pop_macro("alignof")
+
 #undef GSL_MSVC_HAS_VARIADIC_CTOR_BUG
 
 #endif // _MSC_VER <= 1800
diff --git a/include/string_span.h b/include/string_span.h
index fdcbf31..e18e07a 100644
--- a/include/string_span.h
+++ b/include/string_span.h
@@ -22,6 +22,7 @@
 #include "gsl_assert.h"
 #include "gsl_util.h"
 #include "span.h"
+#include <cstdint>
 #include <cstring>
 #include <string>
 
@@ -36,8 +37,7 @@
 // blanket turn off warnings from CppCoreCheck for now
 // so people aren't annoyed by them when running the tool.
 // more targeted suppressions will be added in a future update to the GSL
-#pragma warning(disable: 26481 26482 26483 26485 26490 26491 26492 26493 26495)
-
+#pragma warning(disable : 26481 26482 26483 26485 26490 26491 26492 26493 26495)
 
 // VS 2013 workarounds
 #if _MSC_VER <= 1800
@@ -80,19 +80,19 @@ namespace gsl
 // (sometimes needlessly) break existing programs when introduced.
 //
 
-template<typename CharT, std::ptrdiff_t Extent = dynamic_range>
+template <typename CharT, std::ptrdiff_t Extent = dynamic_extent>
 using basic_zstring = CharT*;
 
-template<std::ptrdiff_t Extent = dynamic_range>
+template <std::ptrdiff_t Extent = dynamic_extent>
 using czstring = basic_zstring<const char, Extent>;
 
-template<std::ptrdiff_t Extent = dynamic_range>
+template <std::ptrdiff_t Extent = dynamic_extent>
 using cwzstring = basic_zstring<const wchar_t, Extent>;
 
-template<std::ptrdiff_t Extent = dynamic_range>
+template <std::ptrdiff_t Extent = dynamic_extent>
 using zstring = basic_zstring<char, Extent>;
 
-template<std::ptrdiff_t Extent = dynamic_range>
+template <std::ptrdiff_t Extent = dynamic_extent>
 using wzstring = basic_zstring<wchar_t, Extent>;
 
 //
@@ -103,85 +103,93 @@ using wzstring = basic_zstring<wchar_t, Extent>;
 //
 // Will fail-fast if sentinel cannot be found before max elements are examined.
 //
-template<typename T, const T Sentinel>
-span<T, dynamic_range> ensure_sentinel(T* seq, std::ptrdiff_t max = PTRDIFF_MAX)
+template <typename T, const T Sentinel>
+span<T, dynamic_extent> ensure_sentinel(T* seq, std::ptrdiff_t max = PTRDIFF_MAX)
 {
     auto cur = seq;
     while ((cur - seq) < max && *cur != Sentinel) ++cur;
     Ensures(*cur == Sentinel);
-    return{ seq, cur - seq };
+    return {seq, cur - seq};
 }
 
-
 //
 // ensure_z - creates a span for a czstring or cwzstring.
 // Will fail fast if a null-terminator cannot be found before
 // the limit of size_type.
 //
-template<typename T>
-inline span<T, dynamic_range> ensure_z(T* const & sz, std::ptrdiff_t max = PTRDIFF_MAX)
+template <typename T>
+inline span<T, dynamic_extent> ensure_z(T* const& sz, std::ptrdiff_t max = PTRDIFF_MAX)
 {
     return ensure_sentinel<T, 0>(sz, max);
 }
 
-// TODO (neilmac) there is probably a better template-magic way to get the const and non-const overloads to share an implementation
-inline span<char, dynamic_range> ensure_z(char* const& sz, std::ptrdiff_t max)
+// TODO (neilmac) there is probably a better template-magic way to get the const and non-const
+// overloads to share an implementation
+inline span<char, dynamic_extent> ensure_z(char* const& sz, std::ptrdiff_t max)
 {
     auto len = strnlen(sz, narrow_cast<size_t>(max));
     Ensures(sz[len] == 0);
-    return{ sz, static_cast<std::ptrdiff_t>(len) };
+    return {sz, static_cast<std::ptrdiff_t>(len)};
 }
 
-inline span<const char, dynamic_range> ensure_z(const char* const& sz, std::ptrdiff_t max)
+inline span<const char, dynamic_extent> ensure_z(const char* const& sz, std::ptrdiff_t max)
 {
     auto len = strnlen(sz, narrow_cast<size_t>(max));
     Ensures(sz[len] == 0);
-    return{ sz, static_cast<std::ptrdiff_t>(len) };
+    return {sz, static_cast<std::ptrdiff_t>(len)};
 }
 
-inline span<wchar_t, dynamic_range> ensure_z(wchar_t* const& sz, std::ptrdiff_t max)
+inline span<wchar_t, dynamic_extent> ensure_z(wchar_t* const& sz, std::ptrdiff_t max)
 {
     auto len = wcsnlen(sz, narrow_cast<size_t>(max));
     Ensures(sz[len] == 0);
-    return{ sz, static_cast<std::ptrdiff_t>(len) };
+    return {sz, static_cast<std::ptrdiff_t>(len)};
 }
 
-inline span<const wchar_t, dynamic_range> ensure_z(const wchar_t* const& sz, std::ptrdiff_t max)
+inline span<const wchar_t, dynamic_extent> ensure_z(const wchar_t* const& sz, std::ptrdiff_t max)
 {
     auto len = wcsnlen(sz, narrow_cast<size_t>(max));
     Ensures(sz[len] == 0);
-    return{ sz, static_cast<std::ptrdiff_t>(len) };
+    return {sz, static_cast<std::ptrdiff_t>(len)};
 }
 
-template<typename T, size_t N>
-span<T, dynamic_range> ensure_z(T(&sz)[N]) { return ensure_z(&sz[0], static_cast<std::ptrdiff_t>(N)); }
+template <typename T, size_t N>
+span<T, dynamic_extent> ensure_z(T (&sz)[N])
+{
+    return ensure_z(&sz[0], static_cast<std::ptrdiff_t>(N));
+}
 
-template<class Cont>
-span<typename std::remove_pointer<typename Cont::pointer>::type, dynamic_range> ensure_z(Cont& cont)
+template <class Cont>
+span<typename std::remove_pointer<typename Cont::pointer>::type, dynamic_extent>
+ensure_z(Cont& cont)
 {
     return ensure_z(cont.data(), static_cast<std::ptrdiff_t>(cont.length()));
 }
 
-template<typename CharT, std::ptrdiff_t>
+template <typename CharT, std::ptrdiff_t>
 class basic_string_span;
 
 namespace details
 {
     template <typename T>
     struct is_basic_string_span_oracle : std::false_type
-    {};
+    {
+    };
 
     template <typename CharT, std::ptrdiff_t Extent>
     struct is_basic_string_span_oracle<basic_string_span<CharT, Extent>> : std::true_type
-    {};
+    {
+    };
 
     template <typename T>
     struct is_basic_string_span : is_basic_string_span_oracle<std::remove_cv_t<T>>
-    {};
+    {
+    };
 
     template <typename T>
     struct length_func
-    {};
+    {
+    };
 
     template <>
     struct length_func<char>
@@ -220,53 +228,46 @@ namespace details
     };
 }
 
-
 //
 // string_span and relatives
 //
-// Note that Extent is always single-dimension only
-//
-template <typename CharT, std::ptrdiff_t Extent = dynamic_range>
+template <typename CharT, std::ptrdiff_t Extent = dynamic_extent>
 class basic_string_span
 {
 public:
-    using value_type = CharT;
-    using const_value_type = std::add_const_t<value_type>;
-    using pointer = std::add_pointer_t<value_type>;
-    using reference = std::add_lvalue_reference_t<value_type>;
-    using const_reference = std::add_lvalue_reference_t<const_value_type>;
-    using bounds_type = static_bounds<Extent>;
-    using impl_type = span<value_type, Extent>;
+    using element_type = CharT;
+    using pointer = std::add_pointer_t<element_type>;
+    using reference = std::add_lvalue_reference_t<element_type>;
+    using const_reference = std::add_lvalue_reference_t<std::add_const_t<element_type>>;
+    using impl_type = span<element_type, Extent>;
 
-    using size_type = ptrdiff_t;
+    using index_type = typename impl_type::index_type;
     using iterator = typename impl_type::iterator;
     using const_iterator = typename impl_type::const_iterator;
     using reverse_iterator = typename impl_type::reverse_iterator;
     using const_reverse_iterator = typename impl_type::const_reverse_iterator;
 
     // default (empty)
-    constexpr basic_string_span() = default;
+    constexpr basic_string_span() noexcept = default;
 
     // copy
-    constexpr basic_string_span(const basic_string_span& other) = default;
+    constexpr basic_string_span(const basic_string_span& other) noexcept = default;
 
-    // move
+// move
 #ifndef GSL_MSVC_NO_DEFAULT_MOVE_CTOR
-    constexpr basic_string_span(basic_string_span&& other) = default;
+    constexpr basic_string_span(basic_string_span&& other) noexcept = default;
 #else
-    constexpr basic_string_span(basic_string_span&& other)
-    	: span_(std::move(other.span_))
-    {}
+    constexpr basic_string_span(basic_string_span&& other) : span_(std::move(other.span_)) {}
 #endif
 
     // assign
-    constexpr basic_string_span& operator=(const basic_string_span& other) = default;
+    constexpr basic_string_span& operator=(const basic_string_span& other) noexcept = default;
 
-    // move assign
+// move assign
 #ifndef GSL_MSVC_NO_DEFAULT_MOVE_CTOR
-    constexpr basic_string_span& operator=(basic_string_span&& other) = default;
+    constexpr basic_string_span& operator=(basic_string_span&& other) noexcept = default;
 #else
-    constexpr basic_string_span& operator=(basic_string_span&& other)
+    constexpr basic_string_span& operator=(basic_string_span&& other) noexcept
     {
         span_ = std::move(other.span_);
         return *this;
@@ -274,211 +275,137 @@ public:
 #endif
 
     // from nullptr
-    constexpr basic_string_span(std::nullptr_t ptr) noexcept
-        : span_(ptr)
-    {}
+    constexpr basic_string_span(std::nullptr_t ptr) noexcept : span_(ptr) {}
 
-    // from nullptr and length
-    constexpr basic_string_span(std::nullptr_t ptr, size_type length) noexcept
-        : span_(ptr, length)
-    {}
+    constexpr basic_string_span(pointer ptr, index_type length) : span_(ptr, length) {}
+    constexpr basic_string_span(pointer firstElem, pointer lastElem) : span_(firstElem, lastElem) {}
 
     // From static arrays - if 0-terminated, remove 0 from the view
+    // All other containers allow 0s within the length, so we do not remove them
+    template <size_t N>
+    constexpr basic_string_span(element_type (&arr)[N]) : span_(remove_z(arr))
+    {
+    }
 
-    // from static arrays and string literals
-    template<size_t N>
-    constexpr basic_string_span(value_type(&arr)[N]) noexcept
-        : span_(remove_z(arr))
-    {}
+    template <size_t N, class ArrayElementType = std::remove_const_t<element_type>>
+    constexpr basic_string_span(std::array<ArrayElementType, N>& arr) noexcept : span_(arr)
+    {
+    }
 
-    // Those allow 0s within the length, so we do not remove them
+    template <size_t N, class ArrayElementType = std::remove_const_t<element_type>>
+    constexpr basic_string_span(const std::array<ArrayElementType, N>& arr) noexcept : span_(arr)
+    {
+    }
 
-    // from raw data and length
-    constexpr basic_string_span(pointer ptr, size_type length) noexcept
-        : span_(ptr, length)
-    {}
+    // Container signature should work for basic_string after C++17 version exists
+    template <class Traits, class Allocator>
+    constexpr basic_string_span(std::basic_string<element_type, Traits, Allocator>& str)
+        : span_(&str[0], str.length())
+    {
+    }
 
-    // from string
-    constexpr basic_string_span(std::string& s) noexcept
-        : span_(const_cast<pointer>(s.data()), narrow_cast<std::ptrdiff_t>(s.length()))
-    {}
+    template <class Traits, class Allocator>
+    constexpr basic_string_span(const std::basic_string<element_type, Traits, Allocator>& str)
+        : span_(&str[0], str.length())
+    {
+    }
 
-    // from containers. Containers must have .size() and .data() function signatures
-    template <typename Cont, typename DataType = typename Cont::value_type,
-        typename Dummy = std::enable_if_t<!details::is_span<Cont>::value
-        && !details::is_basic_string_span<Cont>::value
-        && !(!std::is_const<value_type>::value && std::is_const<Cont>::value) // no converting const containers to non-const span
-        && std::is_convertible<DataType*, value_type*>::value
-        && std::is_same<std::decay_t<decltype(std::declval<Cont>().size(), *std::declval<Cont>().data())>, DataType>::value>
-    >
-    constexpr basic_string_span(Cont& cont)
-        : span_(cont.data(), cont.size())
-    {}
+    // from containers. Containers must have a pointer type and data() function signatures
+    template <class Container,
+              class = std::enable_if_t<
+                  !details::is_basic_string_span<Container>::value &&
+                  std::is_convertible<typename Container::pointer, pointer>::value &&
+                  std::is_convertible<typename Container::pointer,
+                                      decltype(std::declval<Container>().data())>::value>>
+    constexpr basic_string_span(Container& cont) : span_(cont)
+    {
+    }
 
-    // disallow creation from temporary containers and strings
-    template <typename Cont, typename DataType = typename Cont::value_type,
-        typename Dummy = std::enable_if_t<!details::is_span<Cont>::value
-        && !details::is_basic_string_span<Cont>::value
-        && std::is_convertible<DataType*, value_type*>::value
-        && std::is_same<std::decay_t<decltype(std::declval<Cont>().size(), *std::declval<Cont>().data())>, DataType>::value>
-    >
-    basic_string_span(Cont&& cont) = delete;
-
-#ifndef GSL_MSVC_HAS_SFINAE_SUBSTITUTION_ICE
-    // from span
-    template <typename OtherValueType, std::ptrdiff_t OtherExtent,
-        typename Dummy = std::enable_if_t<
-        std::is_convertible<OtherValueType*, value_type*>::value
-        && std::is_convertible<static_bounds<OtherExtent>, bounds_type>::value>
-    >
-    constexpr basic_string_span(span<OtherValueType, OtherExtent> other) noexcept
-        : span_(other)
-    {}
-#else
-    // from span
-    constexpr basic_string_span(span<value_type, Extent> other) noexcept
-        : span_(other)
-    {}
-        
-    template <typename Dummy = std::enable_if_t<!std::is_same<std::remove_const_t<value_type>, value_type>::value>>
-    constexpr basic_string_span(span<std::remove_const_t<value_type>, Extent> other) noexcept
-        : span_(other)
-    {}
-#endif
+    template <class Container,
+              class = std::enable_if_t<
+                  !details::is_basic_string_span<Container>::value &&
+                  std::is_convertible<typename Container::pointer, pointer>::value &&
+                  std::is_convertible<typename Container::pointer,
+                                      decltype(std::declval<Container>().data())>::value>>
+    constexpr basic_string_span(const Container& cont) : span_(cont)
+    {
+    }
 
     // from string_span
-    template <typename OtherValueType, std::ptrdiff_t OtherExtent,
-        typename OtherBounds = static_bounds<OtherExtent>,
-        typename Dummy = std::enable_if_t<std::is_convertible<OtherValueType*, value_type*>::value && std::is_convertible<OtherBounds, bounds_type>::value>
-    >
-    constexpr basic_string_span(basic_string_span<OtherValueType, OtherExtent> other) noexcept
+    template <
+        class OtherValueType, std::ptrdiff_t OtherExtent,
+        class = std::enable_if_t<std::is_convertible<
+            typename basic_string_span<OtherValueType, OtherExtent>::impl_type, impl_type>::value>>
+    constexpr basic_string_span(basic_string_span<OtherValueType, OtherExtent> other)
         : span_(other.data(), other.length())
-    {}
-
-    constexpr bool empty() const noexcept
     {
-        return length() == 0;
     }
 
-    // first Count elements
-    template<size_type Count>
-    constexpr basic_string_span<value_type, Count> first() const noexcept
+    template <index_type Count>
+    constexpr basic_string_span<element_type, Count> first() const
     {
-        return{ span_.template first<Count>() };
+        return {span_.template first<Count>()};
     }
 
-    constexpr basic_string_span<value_type, dynamic_range> first(size_type count) const noexcept
+    constexpr basic_string_span<element_type, dynamic_extent> first(index_type count) const
     {
-        return{ span_.first(count) };
+        return {span_.first(count)};
     }
 
-    // last Count elements
-    template<size_type Count>
-    constexpr basic_string_span<value_type, Count> last() const noexcept
+    template <index_type Count>
+    constexpr basic_string_span<element_type, Count> last() const
     {
-        return{ span_.template last<Count>() };
+        return {span_.template last<Count>()};
     }
 
-    constexpr basic_string_span<value_type, dynamic_range> last(size_type count) const noexcept
+    constexpr basic_string_span<element_type, dynamic_extent> last(index_type count) const
     {
-        return{ span_.last(count) };
+        return {span_.last(count)};
     }
 
-    // create a subview of Count elements starting from Offset
-    template<size_type Offset, size_type Count>
-    constexpr basic_string_span<value_type, Count> subspan() const noexcept
+    template <index_type Offset, index_type Count>
+    constexpr basic_string_span<element_type, Count> subspan() const
     {
-        return{ span_.template subspan<Offset, Count>() };
+        return {span_.template subspan<Offset, Count>()};
     }
 
-    constexpr basic_string_span<value_type, dynamic_range> subspan(size_type offset, size_type count = dynamic_range) const noexcept
+    constexpr basic_string_span<element_type, dynamic_extent>
+    subspan(index_type offset, index_type count = dynamic_extent) const
     {
-        return{ span_.subspan(offset, count) };
+        return {span_.subspan(offset, count)};
     }
 
-    constexpr reference operator[](size_type idx) const noexcept
-    {
-        return span_[idx];
-    }
+    constexpr reference operator[](index_type idx) const { return span_[idx]; }
+    constexpr reference operator()(index_type idx) const { return span_[idx]; }
 
-    constexpr pointer data() const noexcept
-    {
-        return span_.data();
-    }
+    constexpr pointer data() const { return span_.data(); }
 
-    // length of the span in elements
-    constexpr size_type length() const noexcept
-    {
-        return span_.size();
-    }
+    constexpr index_type length() const noexcept { return span_.size(); }
+    constexpr index_type size() const noexcept { return span_.size(); }
+    constexpr index_type size_bytes() const noexcept { return span_.size_bytes(); }
+    constexpr index_type length_bytes() const noexcept { return span_.length_bytes(); }
+    constexpr bool empty() const noexcept { return size() == 0; }
 
-    // length of the span in elements
-    constexpr size_type size() const noexcept
-    {
-        return span_.size();
-    }
+    constexpr iterator begin() const noexcept { return span_.begin(); }
+    constexpr iterator end() const noexcept { return span_.end(); }
 
-    // length of the span in bytes
-    constexpr size_type size_bytes() const noexcept
-    {
-        return span_.size_bytes();
-    }
+    constexpr const_iterator cbegin() const noexcept { return span_.cbegin(); }
+    constexpr const_iterator cend() const noexcept { return span_.cend(); }
 
-    // length of the span in bytes
-    constexpr size_type length_bytes() const noexcept
-    {
-        return span_.length_bytes();
-    }
+    constexpr reverse_iterator rbegin() const noexcept { return span_.rbegin(); }
+    constexpr reverse_iterator rend() const noexcept { return span_.rend(); }
 
-    constexpr iterator begin() const noexcept
-    {
-        return span_.begin();
-    }
-
-    constexpr iterator end() const noexcept
-    {
-        return span_.end();
-    }
-
-    constexpr const_iterator cbegin() const noexcept
-    {
-        return span_.cbegin();
-    }
-
-    constexpr const_iterator cend() const noexcept
-    {
-        return span_.cend();
-    }
-
-    constexpr reverse_iterator rbegin() const noexcept
-    {
-        return span_.rbegin();
-    }
-
-    constexpr reverse_iterator rend() const noexcept
-    {
-        return span_.rend();
-    }
-
-    constexpr const_reverse_iterator crbegin() const noexcept
-    {
-        return span_.crbegin();
-    }
-
-    constexpr const_reverse_iterator crend() const noexcept
-    {
-        return span_.crend();
-    }
+    constexpr const_reverse_iterator crbegin() const noexcept { return span_.crbegin(); }
+    constexpr const_reverse_iterator crend() const noexcept { return span_.crend(); }
 
 private:
-
-    static impl_type remove_z(pointer const& sz, std::ptrdiff_t max) noexcept
+    static impl_type remove_z(pointer const& sz, std::ptrdiff_t max)
     {
-        return{ sz, details::length_func<value_type>()(sz, max)};
+        return {sz, details::length_func<element_type>()(sz, max)};
     }
 
-    template<size_t N>
-    static impl_type remove_z(value_type(&sz)[N]) noexcept
+    template <size_t N>
+    static impl_type remove_z(element_type (&sz)[N])
     {
         return remove_z(&sz[0], narrow_cast<std::ptrdiff_t>(N));
     }
@@ -486,16 +413,16 @@ private:
     impl_type span_;
 };
 
-template<std::ptrdiff_t Extent = dynamic_range>
+template <std::ptrdiff_t Extent = dynamic_extent>
 using string_span = basic_string_span<char, Extent>;
 
-template<std::ptrdiff_t Extent = dynamic_range>
+template <std::ptrdiff_t Extent = dynamic_extent>
 using cstring_span = basic_string_span<const char, Extent>;
 
-template<std::ptrdiff_t Extent = dynamic_range>
+template <std::ptrdiff_t Extent = dynamic_extent>
 using wstring_span = basic_string_span<wchar_t, Extent>;
 
-template<std::ptrdiff_t Extent = dynamic_range>
+template <std::ptrdiff_t Extent = dynamic_extent>
 using cwstring_span = basic_string_span<const wchar_t, Extent>;
 
 //
@@ -503,39 +430,40 @@ using cwstring_span = basic_string_span<const wchar_t, Extent>;
 //
 #ifndef GSL_MSVC_HAS_TYPE_DEDUCTION_BUG
 
-template<typename CharT, ptrdiff_t Extent>
-std::basic_string<typename std::remove_const<CharT>::type> to_string(basic_string_span<CharT, Extent> view)
+template <typename CharT, std::ptrdiff_t Extent>
+std::basic_string<typename std::remove_const<CharT>::type>
+to_string(basic_string_span<CharT, Extent> view)
 {
-    return{ view.data(), static_cast<size_t>(view.length()) };
+    return {view.data(), static_cast<size_t>(view.length())};
 }
 
 #else
 
 inline std::string to_string(cstring_span<> view)
 {
-    return{ view.data(), static_cast<size_t>(view.length()) };
+    return {view.data(), static_cast<size_t>(view.length())};
 }
 
 inline std::string to_string(string_span<> view)
 {
-    return{ view.data(), static_cast<size_t>(view.length()) };
+    return {view.data(), static_cast<size_t>(view.length())};
 }
 
 inline std::wstring to_string(cwstring_span<> view)
 {
-    return{ view.data(), static_cast<size_t>(view.length()) };
+    return {view.data(), static_cast<size_t>(view.length())};
 }
 
 inline std::wstring to_string(wstring_span<> view)
 {
-    return{ view.data(), static_cast<size_t>(view.length()) };
+    return {view.data(), static_cast<size_t>(view.length())};
 }
 
 #endif
 
 // zero-terminated string span, used to convert
 // zero-terminated spans to legacy strings
-template<typename CharT, std::ptrdiff_t Extent = dynamic_range>
+template <typename CharT, std::ptrdiff_t Extent = dynamic_extent>
 class basic_zstring_span
 {
 public:
@@ -551,29 +479,26 @@ public:
     using impl_type = span<value_type, Extent>;
     using string_span_type = basic_string_span<value_type, Extent>;
 
-    constexpr basic_zstring_span(impl_type span) noexcept
-        : span_(span)
+    constexpr basic_zstring_span(impl_type s) noexcept : span_(s)
     {
         // expects a zero-terminated span
-        Expects(span[span.size() - 1] == '\0');
+        Expects(s[s.size() - 1] == '\0');
     }
 
     // copy
     constexpr basic_zstring_span(const basic_zstring_span& other) = default;
 
-    // move
+// move
 #ifndef GSL_MSVC_NO_DEFAULT_MOVE_CTOR
     constexpr basic_zstring_span(basic_zstring_span&& other) = default;
 #else
-    constexpr basic_zstring_span(basic_zstring_span&& other)
-        : span_(std::move(other.span_))
-    {}
+    constexpr basic_zstring_span(basic_zstring_span&& other) : span_(std::move(other.span_)) {}
 #endif
 
     // assign
     constexpr basic_zstring_span& operator=(const basic_zstring_span& other) = default;
 
-    // move assign
+// move assign
 #ifndef GSL_MSVC_NO_DEFAULT_MOVE_CTOR
     constexpr basic_zstring_span& operator=(basic_zstring_span&& other) = default;
 #else
@@ -586,7 +511,10 @@ public:
 
     constexpr bool empty() const noexcept { return span_.size() == 0; }
 
-    constexpr string_span_type as_string_span() const noexcept { return span_.first(span_.size()-1); }
+    constexpr string_span_type as_string_span() const noexcept
+    {
+        return span_.first(span_.size() - 1);
+    }
 
     constexpr string_span_type ensure_z() const noexcept { return gsl::ensure_z(span_); }
 
@@ -596,28 +524,26 @@ private:
     impl_type span_;
 };
 
-template <std::ptrdiff_t Max = dynamic_range>
+template <std::ptrdiff_t Max = dynamic_extent>
 using zstring_span = basic_zstring_span<char, Max>;
 
-template <std::ptrdiff_t Max = dynamic_range>
+template <std::ptrdiff_t Max = dynamic_extent>
 using wzstring_span = basic_zstring_span<wchar_t, Max>;
 
-template <std::ptrdiff_t Max = dynamic_range>
+template <std::ptrdiff_t Max = dynamic_extent>
 using czstring_span = basic_zstring_span<const char, Max>;
 
-template <std::ptrdiff_t Max = dynamic_range>
+template <std::ptrdiff_t Max = dynamic_extent>
 using cwzstring_span = basic_zstring_span<const wchar_t, Max>;
 
-} // namespace GSL
-
 // operator ==
-template <typename CharT, std::ptrdiff_t Extent = gsl::dynamic_range, typename T,
-    typename = std::enable_if_t<
-    std::is_convertible<T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value>
->
-bool operator==(gsl::basic_string_span<CharT, Extent> one, const T& other) noexcept
+template <class CharT, std::ptrdiff_t Extent, class T,
+          class = std::enable_if_t<
+              details::is_basic_string_span<T>::value ||
+              std::is_convertible<T, gsl::basic_string_span<std::add_const_t<CharT>>>::value>>
+bool operator==(const gsl::basic_string_span<CharT, Extent>& one, const T& other) noexcept
 {
-    gsl::basic_string_span<std::add_const_t<CharT>, Extent> tmp(other);
+    gsl::basic_string_span<std::add_const_t<CharT>> tmp(other);
 #ifdef GSL_MSVC_NO_CPP14_STD_EQUAL
     return (one.size() == tmp.size()) && std::equal(one.begin(), one.end(), tmp.begin());
 #else
@@ -625,14 +551,13 @@ bool operator==(gsl::basic_string_span<CharT, Extent> one, const T& other) noexc
 #endif
 }
 
-template <typename CharT, std::ptrdiff_t Extent = gsl::dynamic_range, typename T,
-    typename Dummy = std::enable_if_t<
-    std::is_convertible<T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value
-    && !gsl::details::is_basic_string_span<T>::value>
->
-bool operator==(const T& one, gsl::basic_string_span<CharT, Extent> other) noexcept
+template <class CharT, std::ptrdiff_t Extent, class T,
+          class = std::enable_if_t<
+              !details::is_basic_string_span<T>::value &&
+              std::is_convertible<T, gsl::basic_string_span<std::add_const_t<CharT>>>::value>>
+bool operator==(const T& one, const gsl::basic_string_span<CharT, Extent>& other) noexcept
 {
-    gsl::basic_string_span<std::add_const_t<CharT>, Extent> tmp(one);
+    gsl::basic_string_span<std::add_const_t<CharT>> tmp(one);
 #ifdef GSL_MSVC_NO_CPP14_STD_EQUAL
     return (tmp.size() == other.size()) && std::equal(tmp.begin(), tmp.end(), other.begin());
 #else
@@ -640,141 +565,73 @@ bool operator==(const T& one, gsl::basic_string_span<CharT, Extent> other) noexc
 #endif
 }
 
-#ifndef _MSC_VER 
-
-// VS treats temp and const containers as convertible to basic_string_span,
-// so the cases below are already covered by the previous operators
-
-template <typename CharT, std::ptrdiff_t Extent = gsl::dynamic_range, typename T,
-    typename DataType = typename T::value_type,
-    typename Dummy = std::enable_if_t<
-    !gsl::details::is_span<T>::value
-    && !gsl::details::is_basic_string_span<T>::value
-    && std::is_convertible<DataType*, CharT*>::value
-    && std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>, DataType>::value>
->
-bool operator==(gsl::basic_string_span<CharT, Extent> one, const T& other) noexcept
-{
-    gsl::basic_string_span<std::add_const_t<CharT>, Extent> tmp(other);
-    return std::equal(one.begin(), one.end(), tmp.begin(), tmp.end());
-}
-
-template <typename CharT, std::ptrdiff_t Extent = gsl::dynamic_range, typename T,
-    typename DataType = typename T::value_type,
-    typename Dummy = std::enable_if_t<
-    !gsl::details::is_span<T>::value
-    && !gsl::details::is_basic_string_span<T>::value
-    && std::is_convertible<DataType*, CharT*>::value
-    && std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>, DataType>::value>
->
-bool operator==(const T& one, gsl::basic_string_span<CharT, Extent> other) noexcept
-{
-    gsl::basic_string_span<std::add_const_t<CharT>, Extent> tmp(one);
-    return std::equal(tmp.begin(), tmp.end(), other.begin(), other.end());
-}
-#endif
-
 // operator !=
-template <typename CharT, std::ptrdiff_t Extent = gsl::dynamic_range, typename T,
-    typename = std::enable_if_t<
-    std::is_convertible<T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value>
->
+template <typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
+          typename = std::enable_if_t<std::is_convertible<
+              T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value>>
 bool operator!=(gsl::basic_string_span<CharT, Extent> one, const T& other) noexcept
 {
     return !(one == other);
 }
 
-template <typename CharT, std::ptrdiff_t Extent = gsl::dynamic_range, typename T,
+template <
+    typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
     typename Dummy = std::enable_if_t<
-    std::is_convertible<T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value
-    && !gsl::details::is_basic_string_span<T>::value>
->
+        std::is_convertible<T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value &&
+        !gsl::details::is_basic_string_span<T>::value>>
 bool operator!=(const T& one, gsl::basic_string_span<CharT, Extent> other) noexcept
 {
     return !(one == other);
 }
 
-#ifndef _MSC_VER 
-
-// VS treats temp and const containers as convertible to basic_string_span,
-// so the cases below are already covered by the previous operators
-
-template <typename CharT, std::ptrdiff_t Extent = gsl::dynamic_range, typename T,
-    typename DataType = typename T::value_type,
-    typename Dummy = std::enable_if_t<
-    !gsl::details::is_span<T>::value
-    && !gsl::details::is_basic_string_span<T>::value
-    && std::is_convertible<DataType*, CharT*>::value
-    && std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>, DataType>::value>
->
-bool operator!=(gsl::basic_string_span<CharT, Extent> one, const T& other) noexcept
-{
-    return !(one == other);
-}
-
-template <typename CharT, std::ptrdiff_t Extent = gsl::dynamic_range, typename T,
-    typename DataType = typename T::value_type,
-    typename Dummy = std::enable_if_t<
-    !gsl::details::is_span<T>::value
-    && !gsl::details::is_basic_string_span<T>::value
-    && std::is_convertible<DataType*, CharT*>::value
-    && std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>, DataType>::value>
->
-bool operator!=(const T& one, gsl::basic_string_span<CharT, Extent> other) noexcept
-{
-    return !(one == other);
-}
-#endif
-
 // operator<
-template <typename CharT, std::ptrdiff_t Extent = gsl::dynamic_range, typename T,
-    typename = std::enable_if_t<
-    std::is_convertible<T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value>
->
+template <typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
+          typename = std::enable_if_t<std::is_convertible<
+              T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value>>
 bool operator<(gsl::basic_string_span<CharT, Extent> one, const T& other) noexcept
 {
     gsl::basic_string_span<std::add_const_t<CharT>, Extent> tmp(other);
     return std::lexicographical_compare(one.begin(), one.end(), tmp.begin(), tmp.end());
 }
 
-template <typename CharT, std::ptrdiff_t Extent = gsl::dynamic_range, typename T,
+template <
+    typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
     typename Dummy = std::enable_if_t<
-    std::is_convertible<T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value
-    && !gsl::details::is_basic_string_span<T>::value>
->
+        std::is_convertible<T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value &&
+        !gsl::details::is_basic_string_span<T>::value>>
 bool operator<(const T& one, gsl::basic_string_span<CharT, Extent> other) noexcept
 {
     gsl::basic_string_span<std::add_const_t<CharT>, Extent> tmp(one);
     return std::lexicographical_compare(tmp.begin(), tmp.end(), other.begin(), other.end());
 }
 
-#ifndef _MSC_VER 
+#ifndef _MSC_VER
 
 // VS treats temp and const containers as convertible to basic_string_span,
 // so the cases below are already covered by the previous operators
 
-template <typename CharT, std::ptrdiff_t Extent = gsl::dynamic_range, typename T,
+template <
+    typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
     typename DataType = typename T::value_type,
     typename Dummy = std::enable_if_t<
-    !gsl::details::is_span<T>::value
-    && !gsl::details::is_basic_string_span<T>::value
-    && std::is_convertible<DataType*, CharT*>::value
-    && std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>, DataType>::value>
->
+        !gsl::details::is_span<T>::value && !gsl::details::is_basic_string_span<T>::value &&
+        std::is_convertible<DataType*, CharT*>::value &&
+        std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>,
+                     DataType>::value>>
 bool operator<(gsl::basic_string_span<CharT, Extent> one, const T& other) noexcept
 {
     gsl::basic_string_span<std::add_const_t<CharT>, Extent> tmp(other);
     return std::lexicographical_compare(one.begin(), one.end(), tmp.begin(), tmp.end());
 }
 
-template <typename CharT, std::ptrdiff_t Extent = gsl::dynamic_range, typename T,
+template <
+    typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
     typename DataType = typename T::value_type,
     typename Dummy = std::enable_if_t<
-    !gsl::details::is_span<T>::value
-    && !gsl::details::is_basic_string_span<T>::value
-    && std::is_convertible<DataType*, CharT*>::value
-    && std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>, DataType>::value>
->
+        !gsl::details::is_span<T>::value && !gsl::details::is_basic_string_span<T>::value &&
+        std::is_convertible<DataType*, CharT*>::value &&
+        std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>,
+                     DataType>::value>>
 bool operator<(const T& one, gsl::basic_string_span<CharT, Extent> other) noexcept
 {
     gsl::basic_string_span<std::add_const_t<CharT>, Extent> tmp(one);
@@ -783,51 +640,50 @@ bool operator<(const T& one, gsl::basic_string_span<CharT, Extent> other) noexce
 #endif
 
 // operator <=
-template <typename CharT, std::ptrdiff_t Extent = gsl::dynamic_range, typename T,
-    typename = std::enable_if_t<
-    std::is_convertible<T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value>
->
+template <typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
+          typename = std::enable_if_t<std::is_convertible<
+              T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value>>
 bool operator<=(gsl::basic_string_span<CharT, Extent> one, const T& other) noexcept
 {
     return !(other < one);
 }
 
-template <typename CharT, std::ptrdiff_t Extent = gsl::dynamic_range, typename T,
+template <
+    typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
     typename Dummy = std::enable_if_t<
-    std::is_convertible<T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value
-    && !gsl::details::is_basic_string_span<T>::value>
->
+        std::is_convertible<T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value &&
+        !gsl::details::is_basic_string_span<T>::value>>
 bool operator<=(const T& one, gsl::basic_string_span<CharT, Extent> other) noexcept
 {
     return !(other < one);
 }
 
-#ifndef _MSC_VER 
+#ifndef _MSC_VER
 
 // VS treats temp and const containers as convertible to basic_string_span,
 // so the cases below are already covered by the previous operators
 
-template <typename CharT, std::ptrdiff_t Extent = gsl::dynamic_range, typename T,
+template <
+    typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
     typename DataType = typename T::value_type,
     typename Dummy = std::enable_if_t<
-    !gsl::details::is_span<T>::value
-    && !gsl::details::is_basic_string_span<T>::value
-    && std::is_convertible<DataType*, CharT*>::value
-    && std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>, DataType>::value>
->
+        !gsl::details::is_span<T>::value && !gsl::details::is_basic_string_span<T>::value &&
+        std::is_convertible<DataType*, CharT*>::value &&
+        std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>,
+                     DataType>::value>>
 bool operator<=(gsl::basic_string_span<CharT, Extent> one, const T& other) noexcept
 {
     return !(other < one);
 }
 
-template <typename CharT, std::ptrdiff_t Extent = gsl::dynamic_range, typename T,
+template <
+    typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
     typename DataType = typename T::value_type,
     typename Dummy = std::enable_if_t<
-    !gsl::details::is_span<T>::value
-    && !gsl::details::is_basic_string_span<T>::value
-    && std::is_convertible<DataType*, CharT*>::value
-    && std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>, DataType>::value>
->
+        !gsl::details::is_span<T>::value && !gsl::details::is_basic_string_span<T>::value &&
+        std::is_convertible<DataType*, CharT*>::value &&
+        std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>,
+                     DataType>::value>>
 bool operator<=(const T& one, gsl::basic_string_span<CharT, Extent> other) noexcept
 {
     return !(other < one);
@@ -835,51 +691,50 @@ bool operator<=(const T& one, gsl::basic_string_span<CharT, Extent> other) noexc
 #endif
 
 // operator>
-template <typename CharT, std::ptrdiff_t Extent = gsl::dynamic_range, typename T,
-    typename = std::enable_if_t<
-    std::is_convertible<T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value>
->
+template <typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
+          typename = std::enable_if_t<std::is_convertible<
+              T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value>>
 bool operator>(gsl::basic_string_span<CharT, Extent> one, const T& other) noexcept
 {
     return other < one;
 }
 
-template <typename CharT, std::ptrdiff_t Extent = gsl::dynamic_range, typename T,
+template <
+    typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
     typename Dummy = std::enable_if_t<
-    std::is_convertible<T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value
-    && !gsl::details::is_basic_string_span<T>::value>
->
+        std::is_convertible<T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value &&
+        !gsl::details::is_basic_string_span<T>::value>>
 bool operator>(const T& one, gsl::basic_string_span<CharT, Extent> other) noexcept
 {
     return other < one;
 }
 
-#ifndef _MSC_VER 
+#ifndef _MSC_VER
 
 // VS treats temp and const containers as convertible to basic_string_span,
 // so the cases below are already covered by the previous operators
 
-template <typename CharT, std::ptrdiff_t Extent = gsl::dynamic_range, typename T,
+template <
+    typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
     typename DataType = typename T::value_type,
     typename Dummy = std::enable_if_t<
-    !gsl::details::is_span<T>::value
-    && !gsl::details::is_basic_string_span<T>::value
-    && std::is_convertible<DataType*, CharT*>::value
-    && std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>, DataType>::value>
->
+        !gsl::details::is_span<T>::value && !gsl::details::is_basic_string_span<T>::value &&
+        std::is_convertible<DataType*, CharT*>::value &&
+        std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>,
+                     DataType>::value>>
 bool operator>(gsl::basic_string_span<CharT, Extent> one, const T& other) noexcept
 {
     return other < one;
 }
 
-template <typename CharT, std::ptrdiff_t Extent = gsl::dynamic_range, typename T,
+template <
+    typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
     typename DataType = typename T::value_type,
     typename Dummy = std::enable_if_t<
-    !gsl::details::is_span<T>::value
-    && !gsl::details::is_basic_string_span<T>::value
-    && std::is_convertible<DataType*, CharT*>::value
-    && std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>, DataType>::value>
->
+        !gsl::details::is_span<T>::value && !gsl::details::is_basic_string_span<T>::value &&
+        std::is_convertible<DataType*, CharT*>::value &&
+        std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>,
+                     DataType>::value>>
 bool operator>(const T& one, gsl::basic_string_span<CharT, Extent> other) noexcept
 {
     return other < one;
@@ -887,56 +742,56 @@ bool operator>(const T& one, gsl::basic_string_span<CharT, Extent> other) noexce
 #endif
 
 // operator >=
-template <typename CharT, std::ptrdiff_t Extent = gsl::dynamic_range, typename T,
-    typename = std::enable_if_t<
-    std::is_convertible<T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value>
->
+template <typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
+          typename = std::enable_if_t<std::is_convertible<
+              T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value>>
 bool operator>=(gsl::basic_string_span<CharT, Extent> one, const T& other) noexcept
 {
     return !(one < other);
 }
 
-template <typename CharT, std::ptrdiff_t Extent = gsl::dynamic_range, typename T,
+template <
+    typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
     typename Dummy = std::enable_if_t<
-    std::is_convertible<T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value
-    && !gsl::details::is_basic_string_span<T>::value>
->
+        std::is_convertible<T, gsl::basic_string_span<std::add_const_t<CharT>, Extent>>::value &&
+        !gsl::details::is_basic_string_span<T>::value>>
 bool operator>=(const T& one, gsl::basic_string_span<CharT, Extent> other) noexcept
 {
     return !(one < other);
 }
 
-#ifndef _MSC_VER 
+#ifndef _MSC_VER
 
 // VS treats temp and const containers as convertible to basic_string_span,
 // so the cases below are already covered by the previous operators
 
-template <typename CharT, std::ptrdiff_t Extent = gsl::dynamic_range, typename T,
+template <
+    typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
     typename DataType = typename T::value_type,
     typename Dummy = std::enable_if_t<
-    !gsl::details::is_span<T>::value
-    && !gsl::details::is_basic_string_span<T>::value
-    && std::is_convertible<DataType*, CharT*>::value
-    && std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>, DataType>::value>
->
+        !gsl::details::is_span<T>::value && !gsl::details::is_basic_string_span<T>::value &&
+        std::is_convertible<DataType*, CharT*>::value &&
+        std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>,
+                     DataType>::value>>
 bool operator>=(gsl::basic_string_span<CharT, Extent> one, const T& other) noexcept
 {
     return !(one < other);
 }
 
-template <typename CharT, std::ptrdiff_t Extent = gsl::dynamic_range, typename T,
+template <
+    typename CharT, std::ptrdiff_t Extent = gsl::dynamic_extent, typename T,
     typename DataType = typename T::value_type,
     typename Dummy = std::enable_if_t<
-    !gsl::details::is_span<T>::value
-    && !gsl::details::is_basic_string_span<T>::value
-    && std::is_convertible<DataType*, CharT*>::value
-    && std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>, DataType>::value>
->
+        !gsl::details::is_span<T>::value && !gsl::details::is_basic_string_span<T>::value &&
+        std::is_convertible<DataType*, CharT*>::value &&
+        std::is_same<std::decay_t<decltype(std::declval<T>().size(), *std::declval<T>().data())>,
+                     DataType>::value>>
 bool operator>=(const T& one, gsl::basic_string_span<CharT, Extent> other) noexcept
 {
     return !(one < other);
 }
 #endif
+} // namespace GSL
 
 #ifdef _MSC_VER
 
diff --git a/tests/CMakeLists.txt b/tests/CMakeLists.txt
index e6527da..79931f7 100644
--- a/tests/CMakeLists.txt
+++ b/tests/CMakeLists.txt
@@ -33,7 +33,7 @@ else()
 endif()
 
 function(add_gsl_test name)
-    add_executable(${name} ${name}.cpp ../include/gsl.h ../include/gsl_assert.h ../include/gsl_util.h ../include/span.h ../include/string_span.h)
+    add_executable(${name} ${name}.cpp ../include/gsl.h ../include/gsl_assert.h ../include/gsl_util.h ../include/multi_span.h ../include/span.h ../include/string_span.h)
     target_link_libraries(${name} UnitTest++)
     install(TARGETS ${name}
         RUNTIME DESTINATION bin
@@ -45,6 +45,7 @@ function(add_gsl_test name)
 endfunction()
 
 add_gsl_test(span_tests)
+add_gsl_test(multi_span_tests)
 add_gsl_test(strided_span_tests)
 add_gsl_test(string_span_tests)
 add_gsl_test(at_tests)
@@ -53,3 +54,4 @@ add_gsl_test(notnull_tests)
 add_gsl_test(assertion_tests)
 add_gsl_test(utils_tests)
 add_gsl_test(owner_tests)
+add_gsl_test(byte_tests)
\ No newline at end of file
diff --git a/tests/bounds_tests.cpp b/tests/bounds_tests.cpp
index 0665260..736a85c 100644
--- a/tests/bounds_tests.cpp
+++ b/tests/bounds_tests.cpp
@@ -15,7 +15,7 @@
 ///////////////////////////////////////////////////////////////////////////////
 
 #include <UnitTest++/UnitTest++.h> 
-#include <span.h>
+#include <multi_span.h>
 #include <vector>
 
 using namespace std;
@@ -58,7 +58,7 @@ SUITE(bounds_test)
 		auto itr = bounds.begin();
 		(void)itr;	
 #ifdef CONFIRM_COMPILATION_ERRORS
-		span<int, 4, dynamic_range, 2> av(nullptr, bounds);
+		multi_span<int, 4, dynamic_range, 2> av(nullptr, bounds);
 	
 		auto itr2 = av.cbegin();
 	
diff --git a/tests/byte_tests.cpp b/tests/byte_tests.cpp
new file mode 100644
index 0000000..5d4e7f6
--- /dev/null
+++ b/tests/byte_tests.cpp
@@ -0,0 +1,93 @@
+///////////////////////////////////////////////////////////////////////////////
+//
+// Copyright (c) 2015 Microsoft Corporation. All rights reserved.
+//
+// This code is licensed under the MIT License (MIT).
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+//
+///////////////////////////////////////////////////////////////////////////////
+
+#include <UnitTest++/UnitTest++.h>
+#include <gsl_byte.h>
+
+#include <iostream>
+#include <list>
+#include <map>
+#include <memory>
+#include <string>
+#include <vector>
+
+using namespace std;
+using namespace gsl;
+
+namespace
+{
+
+SUITE(byte_tests)
+{
+    TEST(construction)
+    {
+        {
+            byte b = static_cast<byte>(4);
+            CHECK(static_cast<unsigned char>(b) == 4);
+        }
+
+        {
+            byte b = byte(12);
+            CHECK(static_cast<unsigned char>(b) == 12);
+        }
+
+        // waiting for C++17 enum class direct initializer support
+        //{
+        //    byte b { 14 };
+        //    CHECK(static_cast<unsigned char>(b) == 14);
+        //}
+    }
+
+    TEST(bitwise_operations)
+    {
+        byte b = byte(0xFF);
+
+        byte a = byte(0x00);
+        CHECK((b | a) == byte(0xFF));
+        CHECK(a == byte(0x00));
+
+        a |= b;
+        CHECK(a == byte(0xFF));
+
+        a = byte(0x01);
+        CHECK((b & a) == byte(0x01));
+
+        a &= b;
+        CHECK(a == byte(0x01));
+
+        CHECK((b ^ a) == byte(0xFE));
+        
+        CHECK(a == byte(0x01));
+        a ^= b;
+        CHECK(a == byte(0xFE));
+
+        a = byte(0x01);
+        CHECK(~a == byte(0xFE));
+
+        a = byte(0xFF);
+        CHECK((a << 4) == byte(0xF0));
+        CHECK((a >> 4) == byte(0x0F));
+
+        a <<= 4;
+        CHECK(a == byte(0xF0));
+        a >>= 4;
+        CHECK(a == byte(0x0F));
+    }
+}
+
+}
+
+int main(int, const char* []) { return UnitTest::RunAllTests(); }
diff --git a/tests/multi_span_tests.cpp b/tests/multi_span_tests.cpp
new file mode 100644
index 0000000..7432057
--- /dev/null
+++ b/tests/multi_span_tests.cpp
@@ -0,0 +1,1679 @@
+///////////////////////////////////////////////////////////////////////////////
+//
+// Copyright (c) 2015 Microsoft Corporation. All rights reserved.
+//
+// This code is licensed under the MIT License (MIT).
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+//
+///////////////////////////////////////////////////////////////////////////////
+
+#include <UnitTest++/UnitTest++.h>
+#include <multi_span.h>
+
+#include <iostream>
+#include <list>
+#include <map>
+#include <memory>
+#include <string>
+#include <vector>
+
+using namespace std;
+using namespace gsl;
+
+namespace
+{
+struct BaseClass
+{
+};
+struct DerivedClass : BaseClass
+{
+};
+}
+
+SUITE(multi_span_tests)
+{
+
+    TEST(default_constructor)
+    {
+        {
+            multi_span<int> s;
+            CHECK(s.length() == 0 && s.data() == nullptr);
+
+            multi_span<const int> cs;
+            CHECK(cs.length() == 0 && cs.data() == nullptr);
+        }
+
+        {
+            multi_span<int, 0> s;
+            CHECK(s.length() == 0 && s.data() == nullptr);
+
+            multi_span<const int, 0> cs;
+            CHECK(cs.length() == 0 && cs.data() == nullptr);
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            multi_span<int, 1> s;
+            CHECK(s.length() == 1 && s.data() == nullptr); // explains why it can't compile
+#endif
+        }
+
+        {
+            multi_span<int> s{};
+            CHECK(s.length() == 0 && s.data() == nullptr);
+
+            multi_span<const int> cs{};
+            CHECK(cs.length() == 0 && cs.data() == nullptr);
+        }
+    }
+
+    TEST(from_nullptr_constructor)
+    {
+        {
+            multi_span<int> s = nullptr;
+            CHECK(s.length() == 0 && s.data() == nullptr);
+
+            multi_span<const int> cs = nullptr;
+            CHECK(cs.length() == 0 && cs.data() == nullptr);
+        }
+
+        {
+            multi_span<int, 0> s = nullptr;
+            CHECK(s.length() == 0 && s.data() == nullptr);
+
+            multi_span<const int, 0> cs = nullptr;
+            CHECK(cs.length() == 0 && cs.data() == nullptr);
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            multi_span<int, 1> s = nullptr;
+            CHECK(s.length() == 1 && s.data() == nullptr); // explains why it can't compile
+#endif
+        }
+
+        {
+            multi_span<int> s{nullptr};
+            CHECK(s.length() == 0 && s.data() == nullptr);
+
+            multi_span<const int> cs{nullptr};
+            CHECK(cs.length() == 0 && cs.data() == nullptr);
+        }
+
+        {
+            multi_span<int*> s{nullptr};
+            CHECK(s.length() == 0 && s.data() == nullptr);
+
+            multi_span<const int*> cs{nullptr};
+            CHECK(cs.length() == 0 && cs.data() == nullptr);
+        }
+    }
+
+    TEST(from_nullptr_length_constructor)
+    {
+        {
+            multi_span<int> s{nullptr, 0};
+            CHECK(s.length() == 0 && s.data() == nullptr);
+
+            multi_span<const int> cs{nullptr, 0};
+            CHECK(cs.length() == 0 && cs.data() == nullptr);
+        }
+
+        {
+            multi_span<int, 0> s{nullptr, 0};
+            CHECK(s.length() == 0 && s.data() == nullptr);
+
+            multi_span<const int, 0> cs{nullptr, 0};
+            CHECK(cs.length() == 0 && cs.data() == nullptr);
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            multi_span<int, 1> s{nullptr, 0};
+            CHECK(s.length() == 1 && s.data() == nullptr); // explains why it can't compile
+#endif
+        }
+
+        {
+            auto workaround_macro = []() { multi_span<int> s{nullptr, 1}; };
+            CHECK_THROW(workaround_macro(), fail_fast);
+
+            auto const_workaround_macro = []() { multi_span<const int> cs{nullptr, 1}; };
+            CHECK_THROW(const_workaround_macro(), fail_fast);
+        }
+
+        {
+            auto workaround_macro = []() { multi_span<int, 0> s{nullptr, 1}; };
+            CHECK_THROW(workaround_macro(), fail_fast);
+
+            auto const_workaround_macro = []() { multi_span<const int, 0> s{nullptr, 1}; };
+            CHECK_THROW(const_workaround_macro(), fail_fast);
+        }
+
+        {
+            multi_span<int*> s{nullptr, 0};
+            CHECK(s.length() == 0 && s.data() == nullptr);
+
+            multi_span<const int*> cs{nullptr, 0};
+            CHECK(cs.length() == 0 && cs.data() == nullptr);
+        }
+    }
+
+    TEST(from_element_constructor)
+    {
+        int i = 5;
+
+        {
+            multi_span<int> s = i;
+            CHECK(s.length() == 1 && s.data() == &i);
+            CHECK(s[0] == 5);
+
+            multi_span<const int> cs = i;
+            CHECK(cs.length() == 1 && cs.data() == &i);
+            CHECK(cs[0] == 5);
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            const j = 1;
+            multi_span<int, 0> s = j;
+#endif
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            multi_span<int, 0> s = i;
+            CHECK(s.length() == 0 && s.data() == &i);
+#endif
+        }
+
+        {
+            multi_span<int, 1> s = i;
+            CHECK(s.length() == 1 && s.data() == &i);
+            CHECK(s[0] == 5);
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            multi_span<int, 2> s = i;
+            CHECK(s.length() == 2 && s.data() == &i);
+#endif
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            auto get_a_temp = []() -> int { return 4; };
+            auto use_a_span = [](multi_span<int> s) { (void) s; };
+            use_a_span(get_a_temp());
+#endif
+        }
+    }
+
+    TEST(from_pointer_length_constructor)
+    {
+        int arr[4] = {1, 2, 3, 4};
+
+        {
+            multi_span<int> s{&arr[0], 2};
+            CHECK(s.length() == 2 && s.data() == &arr[0]);
+            CHECK(s[0] == 1 && s[1] == 2);
+        }
+
+        {
+            multi_span<int, 2> s{&arr[0], 2};
+            CHECK(s.length() == 2 && s.data() == &arr[0]);
+            CHECK(s[0] == 1 && s[1] == 2);
+        }
+
+        {
+            int* p = nullptr;
+            multi_span<int> s{p, 0};
+            CHECK(s.length() == 0 && s.data() == nullptr);
+        }
+
+        {
+            int* p = nullptr;
+            auto workaround_macro = [=]() { multi_span<int> s{p, 2}; };
+            CHECK_THROW(workaround_macro(), fail_fast);
+        }
+    }
+
+    TEST(from_pointer_pointer_constructor)
+    {
+        int arr[4] = {1, 2, 3, 4};
+
+        {
+            multi_span<int> s{&arr[0], &arr[2]};
+            CHECK(s.length() == 2 && s.data() == &arr[0]);
+            CHECK(s[0] == 1 && s[1] == 2);
+        }
+
+        {
+            multi_span<int, 2> s{&arr[0], &arr[2]};
+            CHECK(s.length() == 2 && s.data() == &arr[0]);
+            CHECK(s[0] == 1 && s[1] == 2);
+        }
+
+        {
+            multi_span<int> s{&arr[0], &arr[0]};
+            CHECK(s.length() == 0 && s.data() == &arr[0]);
+        }
+
+        {
+            multi_span<int, 0> s{&arr[0], &arr[0]};
+            CHECK(s.length() == 0 && s.data() == &arr[0]);
+        }
+
+        {
+            auto workaround_macro = [&]() { multi_span<int> s{&arr[1], &arr[0]}; };
+            CHECK_THROW(workaround_macro(), fail_fast);
+        }
+
+        {
+            int* p = nullptr;
+            auto workaround_macro = [&]() { multi_span<int> s{&arr[0], p}; };
+            CHECK_THROW(workaround_macro(), fail_fast);
+        }
+
+        {
+            int* p = nullptr;
+            auto workaround_macro = [&]() { multi_span<int> s{p, p}; };
+            CHECK_THROW(workaround_macro(), fail_fast);
+        }
+
+        {
+            int* p = nullptr;
+            auto workaround_macro = [&]() { multi_span<int> s{&arr[0], p}; };
+            CHECK_THROW(workaround_macro(), fail_fast);
+        }
+    }
+
+    TEST(from_array_constructor)
+    {
+        int arr[5] = {1, 2, 3, 4, 5};
+
+        {
+            multi_span<int> s{arr};
+            CHECK(s.length() == 5 && s.data() == &arr[0]);
+        }
+
+        {
+            multi_span<int, 5> s{arr};
+            CHECK(s.length() == 5 && s.data() == &arr[0]);
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            multi_span<int, 6> s{arr};
+#endif
+        }
+
+        {
+            multi_span<int, 0> s{arr};
+            CHECK(s.length() == 0 && s.data() == &arr[0]);
+        }
+
+        int arr2d[2][3] = {1, 2, 3, 4, 5, 6};
+
+        {
+            multi_span<int> s{arr2d};
+            CHECK(s.length() == 6 && s.data() == &arr2d[0][0]);
+            CHECK(s[0] == 1 && s[5] == 6);
+        }
+
+        {
+            multi_span<int, 0> s{arr2d};
+            CHECK(s.length() == 0 && s.data() == &arr2d[0][0]);
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            multi_span<int, 5> s{arr2d};
+#endif
+        }
+
+        {
+            multi_span<int, 6> s{arr2d};
+            CHECK(s.length() == 6 && s.data() == &arr2d[0][0]);
+            CHECK(s[0] == 1 && s[5] == 6);
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            multi_span<int, 7> s{arr2d};
+#endif
+        }
+
+        {
+            multi_span<int[3]> s{arr2d[0]};
+            CHECK(s.length() == 1 && s.data() == &arr2d[0]);
+        }
+
+        {
+            multi_span<int, 2, 3> s{arr2d};
+            CHECK(s.length() == 6 && s.data() == &arr2d[0][0]);
+            auto workaround_macro = [&]() { return s[{1, 2}] == 6; };
+            CHECK(workaround_macro());
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            multi_span<int, 3, 3> s{arr2d};
+#endif
+        }
+
+        int arr3d[2][3][2] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12};
+
+        {
+            multi_span<int> s{arr3d};
+            CHECK(s.length() == 12 && s.data() == &arr3d[0][0][0]);
+            CHECK(s[0] == 1 && s[11] == 12);
+        }
+
+        {
+            multi_span<int, 0> s{arr3d};
+            CHECK(s.length() == 0 && s.data() == &arr3d[0][0][0]);
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            multi_span<int, 11> s{arr3d};
+#endif
+        }
+
+        {
+            multi_span<int, 12> s{arr3d};
+            CHECK(s.length() == 12 && s.data() == &arr3d[0][0][0]);
+            CHECK(s[0] == 1 && s[5] == 6);
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            multi_span<int, 13> s{arr3d};
+#endif
+        }
+
+        {
+            multi_span<int[3][2]> s{arr3d[0]};
+            CHECK(s.length() == 1 && s.data() == &arr3d[0]);
+        }
+
+        {
+            multi_span<int, 3, 2, 2> s{arr3d};
+            CHECK(s.length() == 12 && s.data() == &arr3d[0][0][0]);
+            auto workaround_macro = [&]() { return s[{2, 1, 0}] == 11; };
+            CHECK(workaround_macro());
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            multi_span<int, 3, 3, 3> s{arr3d};
+#endif
+        }
+    }
+
+    TEST(from_dynamic_array_constructor)
+    {
+        double(*arr)[3][4] = new double[100][3][4];
+
+        {
+            multi_span<double, dynamic_range, 3, 4> s(arr, 10);
+            CHECK(s.length() == 120 && s.data() == &arr[0][0][0]);
+            CHECK_THROW(s[10][3][4], fail_fast);
+        }
+
+        {
+            multi_span<double, dynamic_range, 4, 3> s(arr, 10);
+            CHECK(s.length() == 120 && s.data() == &arr[0][0][0]);
+        }
+
+        {
+            multi_span<double> s(arr, 10);
+            CHECK(s.length() == 120 && s.data() == &arr[0][0][0]);
+        }
+
+        {
+            multi_span<double, dynamic_range, 3, 4> s(arr, 0);
+            CHECK(s.length() == 0 && s.data() == &arr[0][0][0]);
+        }
+
+        delete[] arr;
+    }
+
+    TEST(from_std_array_constructor)
+    {
+        std::array<int, 4> arr = {1, 2, 3, 4};
+
+        {
+            multi_span<int> s{arr};
+            CHECK(s.size() == narrow_cast<ptrdiff_t>(arr.size()) && s.data() == arr.data());
+
+            multi_span<const int> cs{arr};
+            CHECK(cs.size() == narrow_cast<ptrdiff_t>(arr.size()) && cs.data() == arr.data());
+        }
+
+        {
+            multi_span<int, 4> s{arr};
+            CHECK(s.size() == narrow_cast<ptrdiff_t>(arr.size()) && s.data() == arr.data());
+
+            multi_span<const int, 4> cs{arr};
+            CHECK(cs.size() == narrow_cast<ptrdiff_t>(arr.size()) && cs.data() == arr.data());
+        }
+
+        {
+            multi_span<int, 2> s{arr};
+            CHECK(s.size() == 2 && s.data() == arr.data());
+
+            multi_span<const int, 2> cs{arr};
+            CHECK(cs.size() == 2 && cs.data() == arr.data());
+        }
+
+        {
+            multi_span<int, 0> s{arr};
+            CHECK(s.size() == 0 && s.data() == arr.data());
+
+            multi_span<const int, 0> cs{arr};
+            CHECK(cs.size() == 0 && cs.data() == arr.data());
+        }
+
+        // TODO This is currently an unsupported scenario. We will come back to it as we revise
+        // the multidimensional interface and what transformations between dimensionality look like
+        //{
+        //    multi_span<int, 2, 2> s{arr};
+        //    CHECK(s.size() == narrow_cast<ptrdiff_t>(arr.size()) && s.data() == arr.data());
+        //}
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            multi_span<int, 5> s{arr};
+#endif
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            auto get_an_array = []() { return std::array<int, 4>{1, 2, 3, 4}; };
+            auto take_a_span = [](multi_span<int> s) { (void) s; };
+            // try to take a temporary std::array
+            take_a_span(get_an_array());
+#endif
+        }
+    }
+
+    TEST(from_const_std_array_constructor)
+    {
+        const std::array<int, 4> arr = {1, 2, 3, 4};
+
+        {
+            multi_span<const int> s{arr};
+            CHECK(s.size() == narrow_cast<ptrdiff_t>(arr.size()) && s.data() == arr.data());
+        }
+
+        {
+            multi_span<const int, 4> s{arr};
+            CHECK(s.size() == narrow_cast<ptrdiff_t>(arr.size()) && s.data() == arr.data());
+        }
+
+        {
+            multi_span<const int, 2> s{arr};
+            CHECK(s.size() == 2 && s.data() == arr.data());
+        }
+
+        {
+            multi_span<const int, 0> s{arr};
+            CHECK(s.size() == 0 && s.data() == arr.data());
+        }
+
+        // TODO This is currently an unsupported scenario. We will come back to it as we revise
+        // the multidimensional interface and what transformations between dimensionality look like
+        //{
+        //    multi_span<int, 2, 2> s{arr};
+        //    CHECK(s.size() == narrow_cast<ptrdiff_t>(arr.size()) && s.data() == arr.data());
+        //}
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            multi_span<const int, 5> s{arr};
+#endif
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            auto get_an_array = []() -> const std::array<int, 4> { return {1, 2, 3, 4}; };
+            auto take_a_span = [](multi_span<const int> s) { (void) s; };
+            // try to take a temporary std::array
+            take_a_span(get_an_array());
+#endif
+        }
+    }
+
+    TEST(from_container_constructor)
+    {
+        std::vector<int> v = {1, 2, 3};
+        const std::vector<int> cv = v;
+
+        {
+            multi_span<int> s{v};
+            CHECK(s.size() == narrow_cast<std::ptrdiff_t>(v.size()) && s.data() == v.data());
+
+            multi_span<const int> cs{v};
+            CHECK(cs.size() == narrow_cast<std::ptrdiff_t>(v.size()) && cs.data() == v.data());
+        }
+
+        std::string str = "hello";
+        const std::string cstr = "hello";
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            multi_span<char> s{str};
+            CHECK(s.size() == narrow_cast<std::ptrdiff_t>(str.size()) && s.data() == str.data());
+#endif
+            multi_span<const char> cs{str};
+            CHECK(cs.size() == narrow_cast<std::ptrdiff_t>(str.size()) && cs.data() == str.data());
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            multi_span<char> s{cstr};
+#endif
+            multi_span<const char> cs{cstr};
+            CHECK(cs.size() == narrow_cast<std::ptrdiff_t>(cstr.size()) &&
+                  cs.data() == cstr.data());
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            auto get_temp_vector = []() -> std::vector<int> { return {}; };
+            auto use_span = [](multi_span<int> s) { (void) s; };
+            use_span(get_temp_vector());
+#endif
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            auto get_temp_string = []() -> std::string { return {}; };
+            auto use_span = [](multi_span<char> s) { (void) s; };
+            use_span(get_temp_string());
+#endif
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            auto get_temp_vector = []() -> const std::vector<int> { return {}; };
+            auto use_span = [](multi_span<const char> s) { (void) s; };
+            use_span(get_temp_vector());
+#endif
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            auto get_temp_string = []() -> const std::string { return {}; };
+            auto use_span = [](multi_span<const char> s) { (void) s; };
+            use_span(get_temp_string());
+#endif
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            std::map<int, int> m;
+            multi_span<int> s{m};
+#endif
+        }
+    }
+
+    TEST(from_convertible_span_constructor)
+    {
+#ifdef CONFIRM_COMPILATION_ERRORS
+        multi_span<int, 7, 4, 2> av1(nullptr, b1);
+
+        auto f = [&]() { multi_span<int, 7, 4, 2> av1(nullptr); };
+        CHECK_THROW(f(), fail_fast);
+#endif
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+        static_bounds<size_t, 7, dynamic_range, 2> b12(b11);
+        b12 = b11;
+        b11 = b12;
+
+        multi_span<int, dynamic_range> av1 = nullptr;
+        multi_span<int, 7, dynamic_range, 2> av2(av1);
+        multi_span<int, 7, 4, 2> av2(av1);
+#endif
+
+        multi_span<DerivedClass> avd;
+#ifdef CONFIRM_COMPILATION_ERRORS
+        multi_span<BaseClass> avb = avd;
+#endif
+        multi_span<const DerivedClass> avcd = avd;
+        (void) avcd;
+    }
+
+    TEST(copy_move_and_assignment)
+    {
+        multi_span<int> s1;
+        CHECK(s1.empty());
+
+        int arr[] = {3, 4, 5};
+
+        multi_span<const int> s2 = arr;
+        CHECK(s2.length() == 3 && s2.data() == &arr[0]);
+
+        s2 = s1;
+        CHECK(s2.empty());
+
+        auto get_temp_span = [&]() -> multi_span<int> { return {&arr[1], 2}; };
+        auto use_span = [&](multi_span<const int> s) { CHECK(s.length() == 2 && s.data() == &arr[1]); };
+        use_span(get_temp_span());
+
+        s1 = get_temp_span();
+        CHECK(s1.length() == 2 && s1.data() == &arr[1]);
+    }
+
+    template <class Bounds>
+    void fn(const Bounds&)
+    {
+        static_assert(Bounds::static_size == 60, "static bounds is wrong size");
+    }
+    TEST(as_multi_span_reshape)
+    {
+        int a[3][4][5];
+        auto av = as_multi_span(a);
+        fn(av.bounds());
+        auto av2 = as_multi_span(av, dim<60>());
+        auto av3 = as_multi_span(av2, dim<3>(), dim<4>(), dim<5>());
+        auto av4 = as_multi_span(av3, dim<4>(), dim<>(3), dim<5>());
+        auto av5 = as_multi_span(av4, dim<3>(), dim<4>(), dim<5>());
+        auto av6 = as_multi_span(av5, dim<12>(), dim<>(5));
+
+        fill(av6.begin(), av6.end(), 1);
+
+        auto av7 = as_bytes(av6);
+
+        auto av8 = as_multi_span<int>(av7);
+
+        CHECK(av8.size() == av6.size());
+        for (auto i = 0; i < av8.size(); i++) {
+            CHECK(av8[i] == 1);
+        }
+    }
+
+    TEST(first)
+    {
+        int arr[5] = {1, 2, 3, 4, 5};
+
+        {
+            multi_span<int, 5> av = arr;
+            CHECK((av.first<2>().bounds() == static_bounds<2>()));
+            CHECK(av.first<2>().length() == 2);
+            CHECK(av.first(2).length() == 2);
+        }
+
+        {
+            multi_span<int, 5> av = arr;
+            CHECK((av.first<0>().bounds() == static_bounds<0>()));
+            CHECK(av.first<0>().length() == 0);
+            CHECK(av.first(0).length() == 0);
+        }
+
+        {
+            multi_span<int, 5> av = arr;
+            CHECK((av.first<5>().bounds() == static_bounds<5>()));
+            CHECK(av.first<5>().length() == 5);
+            CHECK(av.first(5).length() == 5);
+        }
+
+        {
+            multi_span<int, 5> av = arr;
+#ifdef CONFIRM_COMPILATION_ERRORS
+            CHECK(av.first<6>().bounds() == static_bounds<6>());
+            CHECK(av.first<6>().length() == 6);
+            CHECK(av.first<-1>().length() == -1);
+#endif
+            CHECK_THROW(av.first(6).length(), fail_fast);
+        }
+
+        {
+            multi_span<int, dynamic_range> av;
+            CHECK((av.first<0>().bounds() == static_bounds<0>()));
+            CHECK(av.first<0>().length() == 0);
+            CHECK(av.first(0).length() == 0);
+        }
+    }
+
+    TEST(last)
+    {
+        int arr[5] = {1, 2, 3, 4, 5};
+
+        {
+            multi_span<int, 5> av = arr;
+            CHECK((av.last<2>().bounds() == static_bounds<2>()));
+            CHECK(av.last<2>().length() == 2);
+            CHECK(av.last(2).length() == 2);
+        }
+
+        {
+            multi_span<int, 5> av = arr;
+            CHECK((av.last<0>().bounds() == static_bounds<0>()));
+            CHECK(av.last<0>().length() == 0);
+            CHECK(av.last(0).length() == 0);
+        }
+
+        {
+            multi_span<int, 5> av = arr;
+            CHECK((av.last<5>().bounds() == static_bounds<5>()));
+            CHECK(av.last<5>().length() == 5);
+            CHECK(av.last(5).length() == 5);
+        }
+
+        {
+            multi_span<int, 5> av = arr;
+#ifdef CONFIRM_COMPILATION_ERRORS
+            CHECK((av.last<6>().bounds() == static_bounds<6>()));
+            CHECK(av.last<6>().length() == 6);
+#endif
+            CHECK_THROW(av.last(6).length(), fail_fast);
+        }
+
+        {
+            multi_span<int, dynamic_range> av;
+            CHECK((av.last<0>().bounds() == static_bounds<0>()));
+            CHECK(av.last<0>().length() == 0);
+            CHECK(av.last(0).length() == 0);
+        }
+    }
+
+    TEST(subspan)
+    {
+        int arr[5] = {1, 2, 3, 4, 5};
+
+        {
+            multi_span<int, 5> av = arr;
+            CHECK((av.subspan<2, 2>().bounds() == static_bounds<2>()));
+            CHECK((av.subspan<2, 2>().length() == 2));
+            CHECK(av.subspan(2, 2).length() == 2);
+            CHECK(av.subspan(2, 3).length() == 3);
+        }
+
+        {
+            multi_span<int, 5> av = arr;
+            CHECK((av.subspan<0, 0>().bounds() == static_bounds<0>()));
+            CHECK((av.subspan<0, 0>().length() == 0));
+            CHECK(av.subspan(0, 0).length() == 0);
+        }
+
+        {
+            multi_span<int, 5> av = arr;
+            CHECK((av.subspan<0, 5>().bounds() == static_bounds<5>()));
+            CHECK((av.subspan<0, 5>().length() == 5));
+            CHECK(av.subspan(0, 5).length() == 5);
+            CHECK_THROW(av.subspan(0, 6).length(), fail_fast);
+            CHECK_THROW(av.subspan(1, 5).length(), fail_fast);
+        }
+
+        {
+            multi_span<int, 5> av = arr;
+            CHECK((av.subspan<5, 0>().bounds() == static_bounds<0>()));
+            CHECK((av.subspan<5, 0>().length() == 0));
+            CHECK(av.subspan(5, 0).length() == 0);
+            CHECK_THROW(av.subspan(6, 0).length(), fail_fast);
+        }
+
+        {
+            multi_span<int, dynamic_range> av;
+            CHECK((av.subspan<0, 0>().bounds() == static_bounds<0>()));
+            CHECK((av.subspan<0, 0>().length() == 0));
+            CHECK(av.subspan(0, 0).length() == 0);
+            CHECK_THROW((av.subspan<1, 0>().length()), fail_fast);
+        }
+
+        {
+            multi_span<int> av;
+            CHECK(av.subspan(0).length() == 0);
+            CHECK_THROW(av.subspan(1).length(), fail_fast);
+        }
+
+        {
+            multi_span<int> av = arr;
+            CHECK(av.subspan(0).length() == 5);
+            CHECK(av.subspan(1).length() == 4);
+            CHECK(av.subspan(4).length() == 1);
+            CHECK(av.subspan(5).length() == 0);
+            CHECK_THROW(av.subspan(6).length(), fail_fast);
+            auto av2 = av.subspan(1);
+            for (int i = 0; i < 4; ++i) CHECK(av2[i] == i + 2);
+        }
+
+        {
+            multi_span<int, 5> av = arr;
+            CHECK(av.subspan(0).length() == 5);
+            CHECK(av.subspan(1).length() == 4);
+            CHECK(av.subspan(4).length() == 1);
+            CHECK(av.subspan(5).length() == 0);
+            CHECK_THROW(av.subspan(6).length(), fail_fast);
+            auto av2 = av.subspan(1);
+            for (int i = 0; i < 4; ++i) CHECK(av2[i] == i + 2);
+        }
+    }
+
+    TEST(rank)
+    {
+        int arr[2] = {1, 2};
+
+        {
+            multi_span<int> s;
+            CHECK(s.rank() == 1);
+        }
+
+        {
+            multi_span<int, 2> s = arr;
+            CHECK(s.rank() == 1);
+        }
+
+        int arr2d[1][1] = {};
+        {
+            multi_span<int, 1, 1> s = arr2d;
+            CHECK(s.rank() == 2);
+        }
+    }
+
+    TEST(extent)
+    {
+        {
+            multi_span<int> s;
+            CHECK(s.extent() == 0);
+            CHECK(s.extent(0) == 0);
+            CHECK_THROW(s.extent(1), fail_fast);
+#ifdef CONFIRM_COMPILATION_ERRORS
+            CHECK(s.extent<1>() == 0);
+#endif
+        }
+
+        {
+            multi_span<int, 0> s;
+            CHECK(s.extent() == 0);
+            CHECK(s.extent(0) == 0);
+            CHECK_THROW(s.extent(1), fail_fast);
+        }
+
+        {
+            int arr2d[1][2] = {};
+
+            multi_span<int, 1, 2> s = arr2d;
+            CHECK(s.extent() == 1);
+            CHECK(s.extent<0>() == 1);
+            CHECK(s.extent<1>() == 2);
+            CHECK(s.extent(0) == 1);
+            CHECK(s.extent(1) == 2);
+            CHECK_THROW(s.extent(3), fail_fast);
+        }
+
+        {
+            int arr2d[1][2] = {};
+
+            multi_span<int, 0, 2> s = arr2d;
+            CHECK(s.extent() == 0);
+            CHECK(s.extent<0>() == 0);
+            CHECK(s.extent<1>() == 2);
+            CHECK(s.extent(0) == 0);
+            CHECK(s.extent(1) == 2);
+            CHECK_THROW(s.extent(3), fail_fast);
+        }
+    }
+
+    TEST(operator_function_call)
+    {
+        int arr[4] = {1, 2, 3, 4};
+
+        {
+            multi_span<int> s = arr;
+            CHECK(s(0) == 1);
+            CHECK_THROW(s(5), fail_fast);
+        }
+
+        int arr2d[2][3] = {1, 2, 3, 4, 5, 6};
+
+        {
+            multi_span<int, 2, 3> s = arr2d;
+            CHECK(s(0, 0) == 1);
+            CHECK(s(1, 2) == 6);
+        }
+    }
+
+    TEST(comparison_operators)
+    {
+        {
+            int arr[10][2];
+            auto s1 = as_multi_span(arr);
+            multi_span<const int, dynamic_range, 2> s2 = s1;
+
+            CHECK(s1 == s2);
+
+            multi_span<int, 20> s3 = as_multi_span(s1, dim<>(20));
+            CHECK(s3 == s2 && s3 == s1);
+        }
+
+        {
+            auto s1 = nullptr;
+            auto s2 = nullptr;
+            CHECK(s1 == s2);
+            CHECK(!(s1 != s2));
+            CHECK(!(s1 < s2));
+            CHECK(s1 <= s2);
+            CHECK(!(s1 > s2));
+            CHECK(s1 >= s2);
+            CHECK(s2 == s1);
+            CHECK(!(s2 != s1));
+            CHECK(!(s2 < s1));
+            CHECK(s2 <= s1);
+            CHECK(!(s2 > s1));
+            CHECK(s2 >= s1);
+        }
+
+        {
+            int arr[] = {2, 1}; // bigger
+
+            multi_span<int> s1 = nullptr;
+            multi_span<int> s2 = arr;
+
+            CHECK(s1 != s2);
+            CHECK(s2 != s1);
+            CHECK(!(s1 == s2));
+            CHECK(!(s2 == s1));
+            CHECK(s1 < s2);
+            CHECK(!(s2 < s1));
+            CHECK(s1 <= s2);
+            CHECK(!(s2 <= s1));
+            CHECK(s2 > s1);
+            CHECK(!(s1 > s2));
+            CHECK(s2 >= s1);
+            CHECK(!(s1 >= s2));
+        }
+
+        {
+            int arr1[] = {1, 2};
+            int arr2[] = {1, 2};
+            multi_span<int> s1 = arr1;
+            multi_span<int> s2 = arr2;
+
+            CHECK(s1 == s2);
+            CHECK(!(s1 != s2));
+            CHECK(!(s1 < s2));
+            CHECK(s1 <= s2);
+            CHECK(!(s1 > s2));
+            CHECK(s1 >= s2);
+            CHECK(s2 == s1);
+            CHECK(!(s2 != s1));
+            CHECK(!(s2 < s1));
+            CHECK(s2 <= s1);
+            CHECK(!(s2 > s1));
+            CHECK(s2 >= s1);
+        }
+
+        {
+            int arr[] = {1, 2, 3};
+
+            multi_span<int> s1 = {&arr[0], 2}; // shorter
+            multi_span<int> s2 = arr; // longer
+
+            CHECK(s1 != s2);
+            CHECK(s2 != s1);
+            CHECK(!(s1 == s2));
+            CHECK(!(s2 == s1));
+            CHECK(s1 < s2);
+            CHECK(!(s2 < s1));
+            CHECK(s1 <= s2);
+            CHECK(!(s2 <= s1));
+            CHECK(s2 > s1);
+            CHECK(!(s1 > s2));
+            CHECK(s2 >= s1);
+            CHECK(!(s1 >= s2));
+        }
+
+        {
+            int arr1[] = {1, 2}; // smaller
+            int arr2[] = {2, 1}; // bigger
+
+            multi_span<int> s1 = arr1;
+            multi_span<int> s2 = arr2;
+
+            CHECK(s1 != s2);
+            CHECK(s2 != s1);
+            CHECK(!(s1 == s2));
+            CHECK(!(s2 == s1));
+            CHECK(s1 < s2);
+            CHECK(!(s2 < s1));
+            CHECK(s1 <= s2);
+            CHECK(!(s2 <= s1));
+            CHECK(s2 > s1);
+            CHECK(!(s1 > s2));
+            CHECK(s2 >= s1);
+            CHECK(!(s1 >= s2));
+        }
+    }
+
+    TEST(basics)
+    {
+        auto ptr = as_multi_span(new int[10], 10);
+        fill(ptr.begin(), ptr.end(), 99);
+        for (int num : ptr) {
+            CHECK(num == 99);
+        }
+
+        delete[] ptr.data();
+    }
+
+    TEST(bounds_checks)
+    {
+        int arr[10][2];
+        auto av = as_multi_span(arr);
+
+        fill(begin(av), end(av), 0);
+
+        av[2][0] = 1;
+        av[1][1] = 3;
+
+        // out of bounds
+        CHECK_THROW(av[1][3] = 3, fail_fast);
+        CHECK_THROW((av[{1, 3}] = 3), fail_fast);
+
+        CHECK_THROW(av[10][2], fail_fast);
+        CHECK_THROW((av[{10, 2}]), fail_fast);
+    }
+
+    void overloaded_func(multi_span<const int, dynamic_range, 3, 5> exp, int expected_value)
+    {
+        for (auto val : exp) {
+            CHECK(val == expected_value);
+        }
+    }
+
+    void overloaded_func(multi_span<const char, dynamic_range, 3, 5> exp, char expected_value)
+    {
+        for (auto val : exp) {
+            CHECK(val == expected_value);
+        }
+    }
+
+    void fixed_func(multi_span<int, 3, 3, 5> exp, int expected_value)
+    {
+        for (auto val : exp) {
+            CHECK(val == expected_value);
+        }
+    }
+
+    TEST(span_parameter_test)
+    {
+        auto data = new int[4][3][5];
+
+        auto av = as_multi_span(data, 4);
+
+        CHECK(av.size() == 60);
+
+        fill(av.begin(), av.end(), 34);
+
+        int count = 0;
+        for_each(av.rbegin(), av.rend(), [&](int val) { count += val; });
+        CHECK(count == 34 * 60);
+        overloaded_func(av, 34);
+
+        overloaded_func(as_multi_span(av, dim<>(4), dim<>(3), dim<>(5)), 34);
+
+        // fixed_func(av, 34);
+        delete[] data;
+    }
+
+    TEST(md_access)
+    {
+        auto width = 5, height = 20;
+
+        auto imgSize = width * height;
+        auto image_ptr = new int[imgSize][3];
+
+        // size check will be done
+        auto image_view =
+            as_multi_span(as_multi_span(image_ptr, imgSize), dim<>(height), dim<>(width), dim<3>());
+
+        iota(image_view.begin(), image_view.end(), 1);
+
+        int expected = 0;
+        for (auto i = 0; i < height; i++) {
+            for (auto j = 0; j < width; j++) {
+                CHECK(expected + 1 == image_view[i][j][0]);
+                CHECK(expected + 2 == image_view[i][j][1]);
+                CHECK(expected + 3 == image_view[i][j][2]);
+
+                auto val = image_view[{i, j, 0}];
+                CHECK(expected + 1 == val);
+                val = image_view[{i, j, 1}];
+                CHECK(expected + 2 == val);
+                val = image_view[{i, j, 2}];
+                CHECK(expected + 3 == val);
+
+                expected += 3;
+            }
+        }
+    }
+
+    TEST(as_multi_span)
+    {
+        {
+            int* arr = new int[150];
+
+            auto av = as_multi_span(arr, dim<10>(), dim<>(3), dim<5>());
+
+            fill(av.begin(), av.end(), 24);
+            overloaded_func(av, 24);
+
+            delete[] arr;
+
+            array<int, 15> stdarr{0};
+            auto av2 = as_multi_span(stdarr);
+            overloaded_func(as_multi_span(av2, dim<>(1), dim<3>(), dim<5>()), 0);
+
+            string str = "ttttttttttttttt"; // size = 15
+            auto t = str.data();
+            (void) t;
+            auto av3 = as_multi_span(str);
+            overloaded_func(as_multi_span(av3, dim<>(1), dim<3>(), dim<5>()), 't');
+        }
+
+        {
+            string str;
+            multi_span<char> strspan = as_multi_span(str);
+            (void) strspan;
+            const string cstr;
+            multi_span<const char> cstrspan = as_multi_span(cstr);
+            (void) cstrspan;
+        }
+
+        {
+            int a[3][4][5];
+            auto av = as_multi_span(a);
+            const int(*b)[4][5];
+            b = a;
+            auto bv = as_multi_span(b, 3);
+
+            CHECK(av == bv);
+
+            const std::array<double, 3> arr = {0.0, 0.0, 0.0};
+            auto cv = as_multi_span(arr);
+            (void) cv;
+
+            vector<float> vec(3);
+            auto dv = as_multi_span(vec);
+            (void) dv;
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+            auto dv2 = as_multi_span(std::move(vec));
+#endif
+        }
+    }
+
+    TEST(empty_spans)
+    {
+        {
+            multi_span<int, 0> empty_av(nullptr);
+
+            CHECK(empty_av.bounds().index_bounds() == index<1>{0});
+            CHECK_THROW(empty_av[0], fail_fast);
+            CHECK_THROW(empty_av.begin()[0], fail_fast);
+            CHECK_THROW(empty_av.cbegin()[0], fail_fast);
+            for (auto& v : empty_av) {
+                (void) v;
+                CHECK(false);
+            }
+        }
+
+        {
+            multi_span<int> empty_av = {};
+            CHECK(empty_av.bounds().index_bounds() == index<1>{0});
+            CHECK_THROW(empty_av[0], fail_fast);
+            CHECK_THROW(empty_av.begin()[0], fail_fast);
+            CHECK_THROW(empty_av.cbegin()[0], fail_fast);
+            for (auto& v : empty_av) {
+                (void) v;
+                CHECK(false);
+            }
+        }
+    }
+
+    TEST(index_constructor)
+    {
+        auto arr = new int[8];
+        for (int i = 0; i < 4; ++i) {
+            arr[2 * i] = 4 + i;
+            arr[2 * i + 1] = i;
+        }
+
+        multi_span<int, dynamic_range> av(arr, 8);
+
+        ptrdiff_t a[1] = {0};
+        index<1> i = a;
+
+        CHECK(av[i] == 4);
+
+        auto av2 = as_multi_span(av, dim<4>(), dim<>(2));
+        ptrdiff_t a2[2] = {0, 1};
+        index<2> i2 = a2;
+
+        CHECK(av2[i2] == 0);
+        CHECK(av2[0][i] == 4);
+
+        delete[] arr;
+    }
+
+    TEST(index_constructors)
+    {
+        {
+            // components of the same type
+            index<3> i1(0, 1, 2);
+            CHECK(i1[0] == 0);
+
+            // components of different types
+            size_t c0 = 0;
+            size_t c1 = 1;
+            index<3> i2(c0, c1, 2);
+            CHECK(i2[0] == 0);
+
+            // from array
+            index<3> i3 = {0, 1, 2};
+            CHECK(i3[0] == 0);
+
+            // from other index of the same size type
+            index<3> i4 = i3;
+            CHECK(i4[0] == 0);
+
+            // default
+            index<3> i7;
+            CHECK(i7[0] == 0);
+
+            // default
+            index<3> i9 = {};
+            CHECK(i9[0] == 0);
+        }
+
+        {
+            // components of the same type
+            index<1> i1(0);
+            CHECK(i1[0] == 0);
+
+            // components of different types
+            size_t c0 = 0;
+            index<1> i2(c0);
+            CHECK(i2[0] == 0);
+
+            // from array
+            index<1> i3 = {0};
+            CHECK(i3[0] == 0);
+
+            // from int
+            index<1> i4 = 0;
+            CHECK(i4[0] == 0);
+
+            // from other index of the same size type
+            index<1> i5 = i3;
+            CHECK(i5[0] == 0);
+
+            // default
+            index<1> i8;
+            CHECK(i8[0] == 0);
+
+            // default
+            index<1> i9 = {};
+            CHECK(i9[0] == 0);
+        }
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+        {
+            index<3> i1(0, 1);
+            index<3> i2(0, 1, 2, 3);
+            index<3> i3 = {0};
+            index<3> i4 = {0, 1, 2, 3};
+            index<1> i5 = {0, 1};
+        }
+#endif
+    }
+
+    TEST(index_operations)
+    {
+        ptrdiff_t a[3] = {0, 1, 2};
+        ptrdiff_t b[3] = {3, 4, 5};
+        index<3> i = a;
+        index<3> j = b;
+
+        CHECK(i[0] == 0);
+        CHECK(i[1] == 1);
+        CHECK(i[2] == 2);
+
+        {
+            index<3> k = i + j;
+
+            CHECK(i[0] == 0);
+            CHECK(i[1] == 1);
+            CHECK(i[2] == 2);
+            CHECK(k[0] == 3);
+            CHECK(k[1] == 5);
+            CHECK(k[2] == 7);
+        }
+
+        {
+            index<3> k = i * 3;
+
+            CHECK(i[0] == 0);
+            CHECK(i[1] == 1);
+            CHECK(i[2] == 2);
+            CHECK(k[0] == 0);
+            CHECK(k[1] == 3);
+            CHECK(k[2] == 6);
+        }
+
+        {
+            index<3> k = 3 * i;
+
+            CHECK(i[0] == 0);
+            CHECK(i[1] == 1);
+            CHECK(i[2] == 2);
+            CHECK(k[0] == 0);
+            CHECK(k[1] == 3);
+            CHECK(k[2] == 6);
+        }
+
+        {
+            index<2> k = details::shift_left(i);
+
+            CHECK(i[0] == 0);
+            CHECK(i[1] == 1);
+            CHECK(i[2] == 2);
+            CHECK(k[0] == 1);
+            CHECK(k[1] == 2);
+        }
+    }
+
+    void iterate_second_column(multi_span<int, dynamic_range, dynamic_range> av)
+    {
+        auto length = av.size() / 2;
+
+        // view to the second column
+        auto section = av.section({0, 1}, {length, 1});
+
+        CHECK(section.size() == length);
+        for (auto i = 0; i < section.size(); ++i) {
+            CHECK(section[i][0] == av[i][1]);
+        }
+
+        for (auto i = 0; i < section.size(); ++i) {
+            auto idx = index<2>{i, 0}; // avoid braces inside the CHECK macro
+            CHECK(section[idx] == av[i][1]);
+        }
+
+        CHECK(section.bounds().index_bounds()[0] == length);
+        CHECK(section.bounds().index_bounds()[1] == 1);
+        for (auto i = 0; i < section.bounds().index_bounds()[0]; ++i) {
+            for (auto j = 0; j < section.bounds().index_bounds()[1]; ++j) {
+                auto idx = index<2>{i, j}; // avoid braces inside the CHECK macro
+                CHECK(section[idx] == av[i][1]);
+            }
+        }
+
+        size_t check_sum = 0;
+        for (auto i = 0; i < length; ++i) {
+            check_sum += av[i][1];
+        }
+
+        {
+            auto idx = 0;
+            size_t sum = 0;
+            for (auto num : section) {
+                CHECK(num == av[idx][1]);
+                sum += num;
+                idx++;
+            }
+
+            CHECK(sum == check_sum);
+        }
+        {
+            size_t idx = length - 1;
+            size_t sum = 0;
+            for (auto iter = section.rbegin(); iter != section.rend(); ++iter) {
+                CHECK(*iter == av[idx][1]);
+                sum += *iter;
+                idx--;
+            }
+
+            CHECK(sum == check_sum);
+        }
+    }
+
+    TEST(span_section_iteration)
+    {
+        int arr[4][2] = {{4, 0}, {5, 1}, {6, 2}, {7, 3}};
+
+        // static bounds
+        {
+            multi_span<int, 4, 2> av = arr;
+            iterate_second_column(av);
+        }
+        // first bound is dynamic
+        {
+            multi_span<int, dynamic_range, 2> av = arr;
+            iterate_second_column(av);
+        }
+        // second bound is dynamic
+        {
+            multi_span<int, 4, dynamic_range> av = arr;
+            iterate_second_column(av);
+        }
+        // both bounds are dynamic
+        {
+            multi_span<int, dynamic_range, dynamic_range> av = arr;
+            iterate_second_column(av);
+        }
+    }
+
+    TEST(dynamic_span_section_iteration)
+    {
+        auto height = 4, width = 2;
+        auto size = height * width;
+
+        auto arr = new int[size];
+        for (auto i = 0; i < size; ++i) {
+            arr[i] = i;
+        }
+
+        auto av = as_multi_span(arr, size);
+
+        // first bound is dynamic
+        {
+            multi_span<int, dynamic_range, 2> av2 = as_multi_span(av, dim<>(height), dim<>(width));
+            iterate_second_column(av2);
+        }
+        // second bound is dynamic
+        {
+            multi_span<int, 4, dynamic_range> av2 = as_multi_span(av, dim<>(height), dim<>(width));
+            iterate_second_column(av2);
+        }
+        // both bounds are dynamic
+        {
+            multi_span<int, dynamic_range, dynamic_range> av2 = as_multi_span(av, dim<>(height), dim<>(width));
+            iterate_second_column(av2);
+        }
+
+        delete[] arr;
+    }
+
+    TEST(span_structure_size)
+    {
+        double(*arr)[3][4] = new double[100][3][4];
+        multi_span<double, dynamic_range, 3, 4> av1(arr, 10);
+
+        struct EffectiveStructure
+        {
+            double* v1;
+            ptrdiff_t v2;
+        };
+        CHECK(sizeof(av1) == sizeof(EffectiveStructure));
+
+        CHECK_THROW(av1[10][3][4], fail_fast);
+
+        multi_span<const double, dynamic_range, 6, 4> av2 = as_multi_span(av1, dim<>(5), dim<6>(), dim<4>());
+        (void) av2;
+    }
+
+    TEST(fixed_size_conversions)
+    {
+        int arr[] = {1, 2, 3, 4};
+
+        // converting to an multi_span from an equal size array is ok
+        multi_span<int, 4> av4 = arr;
+        CHECK(av4.length() == 4);
+
+        // converting to dynamic_range a_v is always ok
+        {
+            multi_span<int, dynamic_range> av = av4;
+            (void) av;
+        }
+        {
+            multi_span<int, dynamic_range> av = arr;
+            (void) av;
+        }
+
+// initialization or assignment to static multi_span that REDUCES size is NOT ok
+#ifdef CONFIRM_COMPILATION_ERRORS
+        {
+            multi_span<int, 2> av2 = arr;
+        }
+        {
+            multi_span<int, 2> av2 = av4;
+        }
+#endif
+
+        {
+            multi_span<int, dynamic_range> av = arr;
+            multi_span<int, 2> av2 = av;
+            (void) av2;
+        }
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+        {
+            multi_span<int, dynamic_range> av = arr;
+            multi_span<int, 2, 1> av2 = av.as_multi_span(dim<2>(), dim<2>());
+        }
+#endif
+
+        {
+            multi_span<int, dynamic_range> av = arr;
+            multi_span<int, 2, 1> av2 = as_multi_span(av, dim<>(2), dim<>(2));
+            auto workaround_macro = [&]() { return av2[{1, 0}] == 2; };
+            CHECK(workaround_macro());
+        }
+
+        // but doing so explicitly is ok
+
+        // you can convert statically
+        {
+            multi_span<int, 2> av2 = {arr, 2};
+            (void) av2;
+        }
+        {
+            multi_span<int, 1> av2 = av4.first<1>();
+            (void) av2;
+        }
+
+        // ...or dynamically
+        {
+            // NB: implicit conversion to multi_span<int,2> from multi_span<int,dynamic_range>
+            multi_span<int, 1> av2 = av4.first(1);
+            (void) av2;
+        }
+
+        // initialization or assignment to static multi_span that requires size INCREASE is not ok.
+        int arr2[2] = {1, 2};
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+        {
+            multi_span<int, 4> av4 = arr2;
+        }
+        {
+            multi_span<int, 2> av2 = arr2;
+            multi_span<int, 4> av4 = av2;
+        }
+#endif
+        {
+            auto f = [&]() {
+                multi_span<int, 4> av9 = {arr2, 2};
+                (void) av9;
+            };
+            CHECK_THROW(f(), fail_fast);
+        }
+
+        // this should fail - we are trying to assign a small dynamic a_v to a fixed_size larger one
+        multi_span<int, dynamic_range> av = arr2;
+        auto f = [&]() {
+            multi_span<int, 4> av2 = av;
+            (void) av2;
+        };
+        CHECK_THROW(f(), fail_fast);
+    }
+
+    TEST(as_writeable_bytes)
+    {
+        int a[] = {1, 2, 3, 4};
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            // you should not be able to get writeable bytes for const objects
+            multi_span<const int, dynamic_range> av = a;
+            auto wav = av.as_writeable_bytes();
+#endif
+        }
+
+        {
+            multi_span<int, dynamic_range> av;
+            auto wav = as_writeable_bytes(av);
+            CHECK(wav.length() == av.length());
+            CHECK(wav.length() == 0);
+            CHECK(wav.size_bytes() == 0);
+        }
+
+        {
+            multi_span<int, dynamic_range> av = a;
+            auto wav = as_writeable_bytes(av);
+            CHECK(wav.data() == (byte*) &a[0]);
+            CHECK(wav.length() == sizeof(a));
+        }
+    }
+
+    TEST(iterator)
+    {
+        int a[] = {1, 2, 3, 4};
+
+        {
+            multi_span<int, dynamic_range> av = a;
+            auto wav = as_writeable_bytes(av);
+            for (auto& b : wav) {
+                b = byte(0);
+            }
+            for (size_t i = 0; i < 4; ++i) {
+                CHECK(a[i] == 0);
+            }
+        }
+
+        {
+            multi_span<int, dynamic_range> av = a;
+            for (auto& n : av) {
+                n = 1;
+            }
+            for (size_t i = 0; i < 4; ++i) {
+                CHECK(a[i] == 1);
+            }
+        }
+    }
+}
+
+int main(int, const char* []) { return UnitTest::RunAllTests(); }
diff --git a/tests/span_tests.cpp b/tests/span_tests.cpp
index 8b39639..8c9829d 100644
--- a/tests/span_tests.cpp
+++ b/tests/span_tests.cpp
@@ -39,7 +39,6 @@ struct DerivedClass : BaseClass
 
 SUITE(span_tests)
 {
-
     TEST(default_constructor)
     {
         {
@@ -74,6 +73,19 @@ SUITE(span_tests)
         }
     }
 
+    TEST(size_optimization)
+    {
+        {
+            span<int> s;
+            CHECK(sizeof(s) == sizeof(int*) + sizeof(ptrdiff_t));
+        }
+
+        {
+            span<int, 0> s;
+            CHECK(sizeof(s) == sizeof(int*));
+        }
+    }
+
     TEST(from_nullptr_constructor)
     {
         {
@@ -119,26 +131,24 @@ SUITE(span_tests)
     TEST(from_nullptr_length_constructor)
     {
         {
-            span<int> s{nullptr, 0};
+            span<int> s{nullptr, static_cast<span<int>::index_type>(0)};
             CHECK(s.length() == 0 && s.data() == nullptr);
 
-            span<const int> cs{nullptr, 0};
+            span<const int> cs{nullptr, static_cast<span<int>::index_type>(0)};
             CHECK(cs.length() == 0 && cs.data() == nullptr);
         }
 
         {
-            span<int, 0> s{nullptr, 0};
+            span<int, 0> s{nullptr, static_cast<span<int>::index_type>(0)};
             CHECK(s.length() == 0 && s.data() == nullptr);
 
-            span<const int, 0> cs{nullptr, 0};
+            span<const int, 0> cs{nullptr, static_cast<span<int>::index_type>(0)};
             CHECK(cs.length() == 0 && cs.data() == nullptr);
         }
 
         {
-#ifdef CONFIRM_COMPILATION_ERRORS
-            span<int, 1> s{nullptr, 0};
-            CHECK(s.length() == 1 && s.data() == nullptr); // explains why it can't compile
-#endif
+            auto workaround_macro = []() { span<int, 1> s{ nullptr, static_cast<span<int>::index_type>(0) }; };
+            CHECK_THROW(workaround_macro(), fail_fast); 
         }
 
         {
@@ -158,64 +168,14 @@ SUITE(span_tests)
         }
 
         {
-            span<int*> s{nullptr, 0};
+            span<int*> s{nullptr, static_cast<span<int>::index_type>(0)};
             CHECK(s.length() == 0 && s.data() == nullptr);
 
-            span<const int*> cs{nullptr, 0};
+            span<const int*> cs{nullptr, static_cast<span<int>::index_type>(0)};
             CHECK(cs.length() == 0 && cs.data() == nullptr);
         }
     }
 
-    TEST(from_element_constructor)
-    {
-        int i = 5;
-
-        {
-            span<int> s = i;
-            CHECK(s.length() == 1 && s.data() == &i);
-            CHECK(s[0] == 5);
-
-            span<const int> cs = i;
-            CHECK(cs.length() == 1 && cs.data() == &i);
-            CHECK(cs[0] == 5);
-        }
-
-        {
-#ifdef CONFIRM_COMPILATION_ERRORS
-            const j = 1;
-            span<int, 0> s = j;
-#endif
-        }
-
-        {
-#ifdef CONFIRM_COMPILATION_ERRORS
-            span<int, 0> s = i;
-            CHECK(s.length() == 0 && s.data() == &i);
-#endif
-        }
-
-        {
-            span<int, 1> s = i;
-            CHECK(s.length() == 1 && s.data() == &i);
-            CHECK(s[0] == 5);
-        }
-
-        {
-#ifdef CONFIRM_COMPILATION_ERRORS
-            span<int, 2> s = i;
-            CHECK(s.length() == 2 && s.data() == &i);
-#endif
-        }
-
-        {
-#ifdef CONFIRM_COMPILATION_ERRORS
-            auto get_a_temp = []() -> int { return 4; };
-            auto use_a_span = [](span<int> s) { (void) s; };
-            use_a_span(get_a_temp());
-#endif
-        }
-    }
-
     TEST(from_pointer_length_constructor)
     {
         int arr[4] = {1, 2, 3, 4};
@@ -234,7 +194,7 @@ SUITE(span_tests)
 
         {
             int* p = nullptr;
-            span<int> s{p, 0};
+            span<int> s{p, static_cast<span<int>::index_type>(0)};
             CHECK(s.length() == 0 && s.data() == nullptr);
         }
 
@@ -271,28 +231,37 @@ SUITE(span_tests)
             CHECK(s.length() == 0 && s.data() == &arr[0]);
         }
 
+        // this will fail the std::distance() precondition, which asserts on MSVC debug builds
+        //{
+        //    auto workaround_macro = [&]() { span<int> s{&arr[1], &arr[0]}; };
+        //    CHECK_THROW(workaround_macro(), fail_fast);
+        //}
+
+        // this will fail the std::distance() precondition, which asserts on MSVC debug builds
+        //{
+        //    int* p = nullptr;
+        //    auto workaround_macro = [&]() { span<int> s{&arr[0], p}; };
+        //    CHECK_THROW(workaround_macro(), fail_fast);
+        //}
+
         {
-            auto workaround_macro = [&]() { span<int> s{&arr[1], &arr[0]}; };
-            CHECK_THROW(workaround_macro(), fail_fast);
+            int* p = nullptr;
+            span<int> s{ p, p };
+            CHECK(s.length() == 0 && s.data() == nullptr);
         }
 
         {
             int* p = nullptr;
-            auto workaround_macro = [&]() { span<int> s{&arr[0], p}; };
-            CHECK_THROW(workaround_macro(), fail_fast);
+            span<int, 0> s{ p, p };
+            CHECK(s.length() == 0 && s.data() == nullptr);
         }
 
-        {
-            int* p = nullptr;
-            auto workaround_macro = [&]() { span<int> s{p, p}; };
-            CHECK_THROW(workaround_macro(), fail_fast);
-        }
-
-        {
-            int* p = nullptr;
-            auto workaround_macro = [&]() { span<int> s{&arr[0], p}; };
-            CHECK_THROW(workaround_macro(), fail_fast);
-        }
+        // this will fail the std::distance() precondition, which asserts on MSVC debug builds
+        //{
+        //    int* p = nullptr;
+        //    auto workaround_macro = [&]() { span<int> s{&arr[0], p}; };
+        //    CHECK_THROW(workaround_macro(), fail_fast);
+        //}
     }
 
     TEST(from_array_constructor)
@@ -309,10 +278,11 @@ SUITE(span_tests)
             CHECK(s.length() == 5 && s.data() == &arr[0]);
         }
 
-        {
+        int arr2d[2][3] = { 1, 2, 3, 4, 5, 6 };
+
 #ifdef CONFIRM_COMPILATION_ERRORS
+        {
             span<int, 6> s{arr};
-#endif
         }
 
         {
@@ -320,8 +290,6 @@ SUITE(span_tests)
             CHECK(s.length() == 0 && s.data() == &arr[0]);
         }
 
-        int arr2d[2][3] = {1, 2, 3, 4, 5, 6};
-
         {
             span<int> s{arr2d};
             CHECK(s.length() == 6 && s.data() == &arr2d[0][0]);
@@ -334,43 +302,17 @@ SUITE(span_tests)
         }
 
         {
-#ifdef CONFIRM_COMPILATION_ERRORS
-            span<int, 5> s{arr2d};
+            span<int, 6> s{ arr2d };
+        }
 #endif
-        }
-
         {
-            span<int, 6> s{arr2d};
-            CHECK(s.length() == 6 && s.data() == &arr2d[0][0]);
-            CHECK(s[0] == 1 && s[5] == 6);
-        }
-
-        {
-#ifdef CONFIRM_COMPILATION_ERRORS
-            span<int, 7> s{arr2d};
-#endif
-        }
-
-        {
-            span<int[3]> s{arr2d[0]};
+            span<int[3]> s{ &(arr2d[0]), 1 };
             CHECK(s.length() == 1 && s.data() == &arr2d[0]);
         }
 
-        {
-            span<int, 2, 3> s{arr2d};
-            CHECK(s.length() == 6 && s.data() == &arr2d[0][0]);
-            auto workaround_macro = [&]() { return s[{1, 2}] == 6; };
-            CHECK(workaround_macro());
-        }
-
-        {
-#ifdef CONFIRM_COMPILATION_ERRORS
-            span<int, 3, 3> s{arr2d};
-#endif
-        }
-
         int arr3d[2][3][2] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12};
 
+#ifdef CONFIRM_COMPILATION_ERRORS
         {
             span<int> s{arr3d};
             CHECK(s.length() == 12 && s.data() == &arr3d[0][0][0]);
@@ -383,9 +325,7 @@ SUITE(span_tests)
         }
 
         {
-#ifdef CONFIRM_COMPILATION_ERRORS
             span<int, 11> s{arr3d};
-#endif
         }
 
         {
@@ -393,30 +333,11 @@ SUITE(span_tests)
             CHECK(s.length() == 12 && s.data() == &arr3d[0][0][0]);
             CHECK(s[0] == 1 && s[5] == 6);
         }
-
-        {
-#ifdef CONFIRM_COMPILATION_ERRORS
-            span<int, 13> s{arr3d};
 #endif
-        }
-
         {
-            span<int[3][2]> s{arr3d[0]};
+            span<int[3][2]> s{&arr3d[0], 1};
             CHECK(s.length() == 1 && s.data() == &arr3d[0]);
         }
-
-        {
-            span<int, 3, 2, 2> s{arr3d};
-            CHECK(s.length() == 12 && s.data() == &arr3d[0][0][0]);
-            auto workaround_macro = [&]() { return s[{2, 1, 0}] == 11; };
-            CHECK(workaround_macro());
-        }
-
-        {
-#ifdef CONFIRM_COMPILATION_ERRORS
-            span<int, 3, 3, 3> s{arr3d};
-#endif
-        }
     }
 
     TEST(from_dynamic_array_constructor)
@@ -424,24 +345,8 @@ SUITE(span_tests)
         double(*arr)[3][4] = new double[100][3][4];
 
         {
-            span<double, dynamic_range, 3, 4> s(arr, 10);
-            CHECK(s.length() == 120 && s.data() == &arr[0][0][0]);
-            CHECK_THROW(s[10][3][4], fail_fast);
-        }
-
-        {
-            span<double, dynamic_range, 4, 3> s(arr, 10);
-            CHECK(s.length() == 120 && s.data() == &arr[0][0][0]);
-        }
-
-        {
-            span<double> s(arr, 10);
-            CHECK(s.length() == 120 && s.data() == &arr[0][0][0]);
-        }
-
-        {
-            span<double, dynamic_range, 3, 4> s(arr, 0);
-            CHECK(s.length() == 0 && s.data() == &arr[0][0][0]);
+            span<double> s(&arr[0][0][0], 10);
+            CHECK(s.length() == 10 && s.data() == &arr[0][0][0]);
         }
 
         delete[] arr;
@@ -467,6 +372,7 @@ SUITE(span_tests)
             CHECK(cs.size() == narrow_cast<ptrdiff_t>(arr.size()) && cs.data() == arr.data());
         }
 
+#ifdef CONFIRM_COMPILATION_ERRORS
         {
             span<int, 2> s{arr};
             CHECK(s.size() == 2 && s.data() == arr.data());
@@ -483,26 +389,23 @@ SUITE(span_tests)
             CHECK(cs.size() == 0 && cs.data() == arr.data());
         }
 
-        // TODO This is currently an unsupported scenario. We will come back to it as we revise
-        // the multidimensional interface and what transformations between dimensionality look like
-        //{
-        //    span<int, 2, 2> s{arr};
-        //    CHECK(s.size() == narrow_cast<ptrdiff_t>(arr.size()) && s.data() == arr.data());
-        //}
-
         {
-#ifdef CONFIRM_COMPILATION_ERRORS
             span<int, 5> s{arr};
-#endif
         }
 
         {
-#ifdef CONFIRM_COMPILATION_ERRORS
-            auto get_an_array = []() { return std::array<int, 4>{1, 2, 3, 4}; };
-            auto take_a_span = [](span<int> s) { (void) s; };
+            auto get_an_array = []()->std::array<int, 4> { return{1, 2, 3, 4}; };
+            auto take_a_span = [](span<int> s) { static_cast<void>(s); };
             // try to take a temporary std::array
             take_a_span(get_an_array());
+        }
 #endif
+
+        {
+            auto get_an_array = []() -> std::array<int, 4> { return { 1, 2, 3, 4 }; };
+            auto take_a_span = [](span<const int> s) { static_cast<void>(s); };
+            // try to take a temporary std::array
+            take_a_span(get_an_array());
         }
     }
 
@@ -519,7 +422,7 @@ SUITE(span_tests)
             span<const int, 4> s{arr};
             CHECK(s.size() == narrow_cast<ptrdiff_t>(arr.size()) && s.data() == arr.data());
         }
-
+#ifdef CONFIRM_COMPILATION_ERRORS
         {
             span<const int, 2> s{arr};
             CHECK(s.size() == 2 && s.data() == arr.data());
@@ -530,27 +433,51 @@ SUITE(span_tests)
             CHECK(s.size() == 0 && s.data() == arr.data());
         }
 
-        // TODO This is currently an unsupported scenario. We will come back to it as we revise
-        // the multidimensional interface and what transformations between dimensionality look like
-        //{
-        //    span<int, 2, 2> s{arr};
-        //    CHECK(s.size() == narrow_cast<ptrdiff_t>(arr.size()) && s.data() == arr.data());
-        //}
-
         {
-#ifdef CONFIRM_COMPILATION_ERRORS
             span<const int, 5> s{arr};
-#endif
         }
 
         {
-#ifdef CONFIRM_COMPILATION_ERRORS
             auto get_an_array = []() -> const std::array<int, 4> { return {1, 2, 3, 4}; };
-            auto take_a_span = [](span<const int> s) { (void) s; };
+            auto take_a_span = [](span<const int> s) { static_cast<void>(s); };
             // try to take a temporary std::array
             take_a_span(get_an_array());
-#endif
         }
+#endif
+    }
+
+    TEST(from_std_array_const_constructor)
+    {
+        std::array<const int, 4> arr = {1, 2, 3, 4};
+
+        {
+            span<const int> s{arr};
+            CHECK(s.size() == narrow_cast<ptrdiff_t>(arr.size()) && s.data() == arr.data());
+        }
+
+        {
+            span<const int, 4> s{arr};
+            CHECK(s.size() == narrow_cast<ptrdiff_t>(arr.size()) && s.data() == arr.data());
+        }
+#ifdef CONFIRM_COMPILATION_ERRORS
+        {
+            span<const int, 2> s{arr};
+            CHECK(s.size() == 2 && s.data() == arr.data());
+        }
+
+        {
+            span<const int, 0> s{arr};
+            CHECK(s.size() == 0 && s.data() == arr.data());
+        }
+
+        {
+            span<const int, 5> s{arr};
+        }
+
+        {
+            span<int, 4> s{arr};
+        }
+#endif
     }
 
     TEST(from_container_constructor)
@@ -590,23 +517,35 @@ SUITE(span_tests)
         {
 #ifdef CONFIRM_COMPILATION_ERRORS
             auto get_temp_vector = []() -> std::vector<int> { return {}; };
-            auto use_span = [](span<int> s) { (void) s; };
+            auto use_span = [](span<int> s) { static_cast<void>(s); };
             use_span(get_temp_vector());
 #endif
         }
 
+        {
+            auto get_temp_vector = []() -> std::vector<int> { return{}; };
+            auto use_span = [](span<const int> s) { static_cast<void>(s); };
+            use_span(get_temp_vector());
+        }
+
         {
 #ifdef CONFIRM_COMPILATION_ERRORS
-            auto get_temp_string = []() -> std::string { return {}; };
-            auto use_span = [](span<char> s) { (void) s; };
+            auto get_temp_string = []() -> std::string { return{}; };
+            auto use_span = [](span<char> s) { static_cast<void>(s); };
             use_span(get_temp_string());
 #endif
         }
 
+        {
+            auto get_temp_string = []() -> std::string { return {}; };
+            auto use_span = [](span<const char> s) { static_cast<void>(s); };
+            use_span(get_temp_string());
+        }
+
         {
 #ifdef CONFIRM_COMPILATION_ERRORS
             auto get_temp_vector = []() -> const std::vector<int> { return {}; };
-            auto use_span = [](span<const char> s) { (void) s; };
+            auto use_span = [](span<const char> s) { static_cast<void>(s); };
             use_span(get_temp_vector());
 #endif
         }
@@ -614,7 +553,7 @@ SUITE(span_tests)
         {
 #ifdef CONFIRM_COMPILATION_ERRORS
             auto get_temp_string = []() -> const std::string { return {}; };
-            auto use_span = [](span<const char> s) { (void) s; };
+            auto use_span = [](span<const char> s) { static_cast<void>(s); };
             use_span(get_temp_string());
 #endif
         }
@@ -629,29 +568,39 @@ SUITE(span_tests)
 
     TEST(from_convertible_span_constructor)
     {
+        {
+            span<DerivedClass> avd;
+            span<const DerivedClass> avcd = avd;
+            static_cast<void>(avcd);
+        }
+
+        {
 #ifdef CONFIRM_COMPILATION_ERRORS
-        span<int, 7, 4, 2> av1(nullptr, b1);
-
-        auto f = [&]() { span<int, 7, 4, 2> av1(nullptr); };
-        CHECK_THROW(f(), fail_fast);
+            span<DerivedClass> avd;
+            span<BaseClass> avb = avd;
+            static_cast<void>(avb);
 #endif
+        }
 
+        {
+            span<int> s;
+            span<unsigned int> s2 = s;
+            static_cast<void>(s2);
+        }
+
+        {
+            span<int> s;
+            span<const unsigned int> s2 = s;
+            static_cast<void>(s2);
+        }
+
+        {
 #ifdef CONFIRM_COMPILATION_ERRORS
-        static_bounds<size_t, 7, dynamic_range, 2> b12(b11);
-        b12 = b11;
-        b11 = b12;
-
-        span<int, dynamic_range> av1 = nullptr;
-        span<int, 7, dynamic_range, 2> av2(av1);
-        span<int, 7, 4, 2> av2(av1);
+            span<int> s;
+            span<short> s2 = s;
+            static_cast<void>(s2);
 #endif
-
-        span<DerivedClass> avd;
-#ifdef CONFIRM_COMPILATION_ERRORS
-        span<BaseClass> avb = avd;
-#endif
-        span<const DerivedClass> avcd = avd;
-        (void) avcd;
+        }
     }
 
     TEST(copy_move_and_assignment)
@@ -675,55 +624,24 @@ SUITE(span_tests)
         CHECK(s1.length() == 2 && s1.data() == &arr[1]);
     }
 
-    template <class Bounds>
-    void fn(const Bounds&)
-    {
-        static_assert(Bounds::static_size == 60, "static bounds is wrong size");
-    }
-    TEST(as_span_reshape)
-    {
-        int a[3][4][5];
-        auto av = as_span(a);
-        fn(av.bounds());
-        auto av2 = as_span(av, dim<60>());
-        auto av3 = as_span(av2, dim<3>(), dim<4>(), dim<5>());
-        auto av4 = as_span(av3, dim<4>(), dim<>(3), dim<5>());
-        auto av5 = as_span(av4, dim<3>(), dim<4>(), dim<5>());
-        auto av6 = as_span(av5, dim<12>(), dim<>(5));
-
-        fill(av6.begin(), av6.end(), 1);
-
-        auto av7 = as_bytes(av6);
-
-        auto av8 = as_span<int>(av7);
-
-        CHECK(av8.size() == av6.size());
-        for (auto i = 0; i < av8.size(); i++) {
-            CHECK(av8[i] == 1);
-        }
-    }
-
     TEST(first)
     {
         int arr[5] = {1, 2, 3, 4, 5};
 
         {
             span<int, 5> av = arr;
-            CHECK((av.first<2>().bounds() == static_bounds<2>()));
             CHECK(av.first<2>().length() == 2);
             CHECK(av.first(2).length() == 2);
         }
 
         {
             span<int, 5> av = arr;
-            CHECK((av.first<0>().bounds() == static_bounds<0>()));
             CHECK(av.first<0>().length() == 0);
             CHECK(av.first(0).length() == 0);
         }
 
         {
             span<int, 5> av = arr;
-            CHECK((av.first<5>().bounds() == static_bounds<5>()));
             CHECK(av.first<5>().length() == 5);
             CHECK(av.first(5).length() == 5);
         }
@@ -731,7 +649,6 @@ SUITE(span_tests)
         {
             span<int, 5> av = arr;
 #ifdef CONFIRM_COMPILATION_ERRORS
-            CHECK(av.first<6>().bounds() == static_bounds<6>());
             CHECK(av.first<6>().length() == 6);
             CHECK(av.first<-1>().length() == -1);
 #endif
@@ -739,8 +656,7 @@ SUITE(span_tests)
         }
 
         {
-            span<int, dynamic_range> av;
-            CHECK((av.first<0>().bounds() == static_bounds<0>()));
+            span<int> av;
             CHECK(av.first<0>().length() == 0);
             CHECK(av.first(0).length() == 0);
         }
@@ -752,21 +668,18 @@ SUITE(span_tests)
 
         {
             span<int, 5> av = arr;
-            CHECK((av.last<2>().bounds() == static_bounds<2>()));
             CHECK(av.last<2>().length() == 2);
             CHECK(av.last(2).length() == 2);
         }
 
         {
             span<int, 5> av = arr;
-            CHECK((av.last<0>().bounds() == static_bounds<0>()));
             CHECK(av.last<0>().length() == 0);
             CHECK(av.last(0).length() == 0);
         }
 
         {
             span<int, 5> av = arr;
-            CHECK((av.last<5>().bounds() == static_bounds<5>()));
             CHECK(av.last<5>().length() == 5);
             CHECK(av.last(5).length() == 5);
         }
@@ -774,15 +687,13 @@ SUITE(span_tests)
         {
             span<int, 5> av = arr;
 #ifdef CONFIRM_COMPILATION_ERRORS
-            CHECK((av.last<6>().bounds() == static_bounds<6>()));
             CHECK(av.last<6>().length() == 6);
 #endif
             CHECK_THROW(av.last(6).length(), fail_fast);
         }
 
         {
-            span<int, dynamic_range> av;
-            CHECK((av.last<0>().bounds() == static_bounds<0>()));
+            span<int> av;
             CHECK(av.last<0>().length() == 0);
             CHECK(av.last(0).length() == 0);
         }
@@ -794,7 +705,6 @@ SUITE(span_tests)
 
         {
             span<int, 5> av = arr;
-            CHECK((av.subspan<2, 2>().bounds() == static_bounds<2>()));
             CHECK((av.subspan<2, 2>().length() == 2));
             CHECK(av.subspan(2, 2).length() == 2);
             CHECK(av.subspan(2, 3).length() == 3);
@@ -802,14 +712,12 @@ SUITE(span_tests)
 
         {
             span<int, 5> av = arr;
-            CHECK((av.subspan<0, 0>().bounds() == static_bounds<0>()));
             CHECK((av.subspan<0, 0>().length() == 0));
             CHECK(av.subspan(0, 0).length() == 0);
         }
 
         {
             span<int, 5> av = arr;
-            CHECK((av.subspan<0, 5>().bounds() == static_bounds<5>()));
             CHECK((av.subspan<0, 5>().length() == 5));
             CHECK(av.subspan(0, 5).length() == 5);
             CHECK_THROW(av.subspan(0, 6).length(), fail_fast);
@@ -818,15 +726,14 @@ SUITE(span_tests)
 
         {
             span<int, 5> av = arr;
-            CHECK((av.subspan<5, 0>().bounds() == static_bounds<0>()));
-            CHECK((av.subspan<5, 0>().length() == 0));
+            CHECK((av.subspan<4, 0>().length() == 0));
+            CHECK(av.subspan(4, 0).length() == 0);
             CHECK(av.subspan(5, 0).length() == 0);
             CHECK_THROW(av.subspan(6, 0).length(), fail_fast);
         }
 
         {
-            span<int, dynamic_range> av;
-            CHECK((av.subspan<0, 0>().bounds() == static_bounds<0>()));
+            span<int> av;
             CHECK((av.subspan<0, 0>().length() == 0));
             CHECK(av.subspan(0, 0).length() == 0);
             CHECK_THROW((av.subspan<1, 0>().length()), fail_fast);
@@ -861,71 +768,6 @@ SUITE(span_tests)
         }
     }
 
-    TEST(rank)
-    {
-        int arr[2] = {1, 2};
-
-        {
-            span<int> s;
-            CHECK(s.rank() == 1);
-        }
-
-        {
-            span<int, 2> s = arr;
-            CHECK(s.rank() == 1);
-        }
-
-        int arr2d[1][1] = {};
-        {
-            span<int, 1, 1> s = arr2d;
-            CHECK(s.rank() == 2);
-        }
-    }
-
-    TEST(extent)
-    {
-        {
-            span<int> s;
-            CHECK(s.extent() == 0);
-            CHECK(s.extent(0) == 0);
-            CHECK_THROW(s.extent(1), fail_fast);
-#ifdef CONFIRM_COMPILATION_ERRORS
-            CHECK(s.extent<1>() == 0);
-#endif
-        }
-
-        {
-            span<int, 0> s;
-            CHECK(s.extent() == 0);
-            CHECK(s.extent(0) == 0);
-            CHECK_THROW(s.extent(1), fail_fast);
-        }
-
-        {
-            int arr2d[1][2] = {};
-
-            span<int, 1, 2> s = arr2d;
-            CHECK(s.extent() == 1);
-            CHECK(s.extent<0>() == 1);
-            CHECK(s.extent<1>() == 2);
-            CHECK(s.extent(0) == 1);
-            CHECK(s.extent(1) == 2);
-            CHECK_THROW(s.extent(3), fail_fast);
-        }
-
-        {
-            int arr2d[1][2] = {};
-
-            span<int, 0, 2> s = arr2d;
-            CHECK(s.extent() == 0);
-            CHECK(s.extent<0>() == 0);
-            CHECK(s.extent<1>() == 2);
-            CHECK(s.extent(0) == 0);
-            CHECK(s.extent(1) == 2);
-            CHECK_THROW(s.extent(3), fail_fast);
-        }
-    }
-
     TEST(operator_function_call)
     {
         int arr[4] = {1, 2, 3, 4};
@@ -936,31 +778,229 @@ SUITE(span_tests)
             CHECK_THROW(s(5), fail_fast);
         }
 
-        int arr2d[2][3] = {1, 2, 3, 4, 5, 6};
-
         {
-            span<int, 2, 3> s = arr2d;
-            CHECK(s(0, 0) == 1);
-            CHECK(s(1, 2) == 6);
+            int arr2d[2] = {1, 6};
+            span<int, 2> s = arr2d;
+            CHECK(s(0) == 1);
+            CHECK(s(1) == 6);
+            CHECK_THROW(s(2) ,fail_fast);
+        }
+    }
+
+    TEST(iterator)
+    {
+        span<int>::iterator it1;
+        span<int>::iterator it2;
+        CHECK(it1 == it2);
+    }
+
+    TEST(const_iterator)
+    {
+        span<int>::const_iterator it1;
+        span<int>::const_iterator it2;
+        CHECK(it1 == it2);
+    }
+
+    TEST(begin_end)
+    {
+        {
+            int a[] = { 1, 2, 3, 4 };
+            span<int> s = a;
+
+            auto it = s.begin();
+            auto first = it;
+            CHECK(it == first);
+            CHECK(*it == 1);
+
+            auto beyond = s.end();
+            CHECK(it != beyond);
+            CHECK_THROW(*beyond, fail_fast);
+
+            CHECK(beyond - first == 4);
+            CHECK(first - first == 0);
+            CHECK(beyond - beyond == 0);
+            
+            ++it;
+            CHECK(it - first == 1);
+            CHECK(*it == 2);
+            *it = 22;
+            CHECK(*it == 22);
+            CHECK(beyond - it == 3);
+
+            it = first;
+            CHECK(it == first);
+            while (it != s.end())
+            {
+                *it = 5;
+                ++it;
+            }
+
+            CHECK(it == beyond);
+            CHECK(it - beyond == 0);
+
+            for (auto& n : s)
+            {
+                CHECK(n == 5);
+            }
+        }
+    }
+
+    TEST(cbegin_cend)
+    {
+        {
+            int a[] = {1, 2, 3, 4};
+            span<int> s = a;
+
+            auto it = s.cbegin();
+            auto first = it;
+            CHECK(it == first);
+            CHECK(*it == 1);
+
+            auto beyond = s.cend();
+            CHECK(it != beyond);
+            CHECK_THROW(*beyond, fail_fast);
+
+            CHECK(beyond - first == 4);
+            CHECK(first - first == 0);
+            CHECK(beyond - beyond == 0);
+
+            ++it;
+            CHECK(it - first == 1);
+            CHECK(*it == 2);
+            *it = 22;
+            CHECK(*it == 22);
+            CHECK(beyond - it == 3);
+
+            it = first;
+            CHECK(it == first);
+            while (it != s.cend())
+            {
+                *it = 5;
+                ++it;
+            }
+
+            CHECK(it == beyond);
+            CHECK(it - beyond == 0);
+
+            for (auto& n : s)
+            {
+                CHECK(n == 5);
+            }
+        }
+    }
+
+    TEST(rbegin_rend)
+    {
+        {
+            int a[] = {1, 2, 3, 4};
+            span<int> s = a;
+
+            auto it = s.rbegin();
+            auto first = it;
+            CHECK(it == first);
+            CHECK(*it == 4);
+
+            auto beyond = s.rend();
+            CHECK(it != beyond);
+            CHECK_THROW(*beyond, fail_fast);
+
+            CHECK(beyond - first == 4);
+            CHECK(first - first == 0);
+            CHECK(beyond - beyond == 0);
+
+            ++it;
+            CHECK(it - first == 1);
+            CHECK(*it == 3);
+            *it = 22;
+            CHECK(*it == 22);
+            CHECK(beyond - it == 3);
+
+            it = first;
+            CHECK(it == first);
+            while (it != s.rend())
+            {
+                *it = 5;
+                ++it;
+            }
+
+            CHECK(it == beyond);
+            CHECK(it - beyond == 0);
+
+            for (auto& n : s)
+            {
+                CHECK(n == 5);
+            }
+        }
+    }
+
+    TEST(crbegin_crend)
+    {
+        {
+            int a[] = {1, 2, 3, 4};
+            span<int> s = a;
+
+            auto it = s.crbegin();
+            auto first = it;
+            CHECK(it == first);
+            CHECK(*it == 4);
+
+            auto beyond = s.crend();
+            CHECK(it != beyond);
+            CHECK_THROW(*beyond, fail_fast);
+
+            CHECK(beyond - first == 4);
+            CHECK(first - first == 0);
+            CHECK(beyond - beyond == 0);
+
+            ++it;
+            CHECK(it - first == 1);
+            CHECK(*it == 3);
+            *it = 22;
+            CHECK(*it == 22);
+            CHECK(beyond - it == 3);
+
+            it = first;
+            CHECK(it == first);
+            while (it != s.crend())
+            {
+                *it = 5;
+                ++it;
+            }
+
+            CHECK(it == beyond);
+            CHECK(it - beyond == 0);
+
+            for (auto& n : s)
+            {
+                CHECK(n == 5);
+            }
         }
     }
 
     TEST(comparison_operators)
     {
         {
-            int arr[10][2];
-            auto s1 = as_span(arr);
-            span<const int, dynamic_range, 2> s2 = s1;
-
+            span<int> s1 = nullptr;
+            span<int> s2 = nullptr;
             CHECK(s1 == s2);
-
-            span<int, 20> s3 = as_span(s1, dim<>(20));
-            CHECK(s3 == s2 && s3 == s1);
+            CHECK(!(s1 != s2));
+            CHECK(!(s1 < s2));
+            CHECK(s1 <= s2);
+            CHECK(!(s1 > s2));
+            CHECK(s1 >= s2);
+            CHECK(s2 == s1);
+            CHECK(!(s2 != s1));
+            CHECK(!(s2 < s1));
+            CHECK(s2 <= s1);
+            CHECK(!(s2 > s1));
+            CHECK(s2 >= s1);
         }
 
         {
-            auto s1 = nullptr;
-            auto s2 = nullptr;
+            int arr[] = {2, 1};
+            span<int> s1 = arr;
+            span<int> s2 = arr;
+
             CHECK(s1 == s2);
             CHECK(!(s1 != s2));
             CHECK(!(s1 < s2));
@@ -1057,570 +1097,36 @@ SUITE(span_tests)
         }
     }
 
-    TEST(basics)
+    TEST(as_bytes)
     {
-        auto ptr = as_span(new int[10], 10);
-        fill(ptr.begin(), ptr.end(), 99);
-        for (int num : ptr) {
-            CHECK(num == 99);
-        }
+        int a[] = {1, 2, 3, 4};
 
-        delete[] ptr.data();
-    }
-
-    TEST(bounds_checks)
-    {
-        int arr[10][2];
-        auto av = as_span(arr);
-
-        fill(begin(av), end(av), 0);
-
-        av[2][0] = 1;
-        av[1][1] = 3;
-
-        // out of bounds
-        CHECK_THROW(av[1][3] = 3, fail_fast);
-        CHECK_THROW((av[{1, 3}] = 3), fail_fast);
-
-        CHECK_THROW(av[10][2], fail_fast);
-        CHECK_THROW((av[{10, 2}]), fail_fast);
-    }
-
-    void overloaded_func(span<const int, dynamic_range, 3, 5> exp, int expected_value)
-    {
-        for (auto val : exp) {
-            CHECK(val == expected_value);
-        }
-    }
-
-    void overloaded_func(span<const char, dynamic_range, 3, 5> exp, char expected_value)
-    {
-        for (auto val : exp) {
-            CHECK(val == expected_value);
-        }
-    }
-
-    void fixed_func(span<int, 3, 3, 5> exp, int expected_value)
-    {
-        for (auto val : exp) {
-            CHECK(val == expected_value);
-        }
-    }
-
-    TEST(span_parameter_test)
-    {
-        auto data = new int[4][3][5];
-
-        auto av = as_span(data, 4);
-
-        CHECK(av.size() == 60);
-
-        fill(av.begin(), av.end(), 34);
-
-        int count = 0;
-        for_each(av.rbegin(), av.rend(), [&](int val) { count += val; });
-        CHECK(count == 34 * 60);
-        overloaded_func(av, 34);
-
-        overloaded_func(as_span(av, dim<>(4), dim<>(3), dim<>(5)), 34);
-
-        // fixed_func(av, 34);
-        delete[] data;
-    }
-
-    TEST(md_access)
-    {
-        auto width = 5, height = 20;
-
-        auto imgSize = width * height;
-        auto image_ptr = new int[imgSize][3];
-
-        // size check will be done
-        auto image_view =
-            as_span(as_span(image_ptr, imgSize), dim<>(height), dim<>(width), dim<3>());
-
-        iota(image_view.begin(), image_view.end(), 1);
-
-        int expected = 0;
-        for (auto i = 0; i < height; i++) {
-            for (auto j = 0; j < width; j++) {
-                CHECK(expected + 1 == image_view[i][j][0]);
-                CHECK(expected + 2 == image_view[i][j][1]);
-                CHECK(expected + 3 == image_view[i][j][2]);
-
-                auto val = image_view[{i, j, 0}];
-                CHECK(expected + 1 == val);
-                val = image_view[{i, j, 1}];
-                CHECK(expected + 2 == val);
-                val = image_view[{i, j, 2}];
-                CHECK(expected + 3 == val);
-
-                expected += 3;
-            }
-        }
-    }
-
-    TEST(as_span)
-    {
         {
-            int* arr = new int[150];
-
-            auto av = as_span(arr, dim<10>(), dim<>(3), dim<5>());
-
-            fill(av.begin(), av.end(), 24);
-            overloaded_func(av, 24);
-
-            delete[] arr;
-
-            array<int, 15> stdarr{0};
-            auto av2 = as_span(stdarr);
-            overloaded_func(as_span(av2, dim<>(1), dim<3>(), dim<5>()), 0);
-
-            string str = "ttttttttttttttt"; // size = 15
-            auto t = str.data();
-            (void) t;
-            auto av3 = as_span(str);
-            overloaded_func(as_span(av3, dim<>(1), dim<3>(), dim<5>()), 't');
+            span<const int> s = a;
+            CHECK(s.length() == 4);
+            span<const byte> bs = as_bytes(s);
+            CHECK(static_cast<const void*>(bs.data()) == static_cast<const void*>(s.data()));
+            CHECK(bs.length() == s.length_bytes());
         }
 
         {
-            string str;
-            span<char> strspan = as_span(str);
-            (void) strspan;
-            const string cstr;
-            span<const char> cstrspan = as_span(cstr);
-            (void) cstrspan;
+            span<int> s;
+            auto bs = as_bytes(s);
+            CHECK(bs.length() == s.length());
+            CHECK(bs.length() == 0);
+            CHECK(bs.size_bytes() == 0);
+            CHECK(static_cast<const void*>(bs.data()) == static_cast<const void*>(s.data()));
+            CHECK(bs.data() == nullptr);
         }
 
         {
-            int a[3][4][5];
-            auto av = as_span(a);
-            const int(*b)[4][5];
-            b = a;
-            auto bv = as_span(b, 3);
-
-            CHECK(av == bv);
-
-            const std::array<double, 3> arr = {0.0, 0.0, 0.0};
-            auto cv = as_span(arr);
-            (void) cv;
-
-            vector<float> vec(3);
-            auto dv = as_span(vec);
-            (void) dv;
-
-#ifdef CONFIRM_COMPILATION_ERRORS
-            auto dv2 = as_span(std::move(vec));
-#endif
+            span<int> s = a;
+            auto bs = as_bytes(s);
+            CHECK(static_cast<const void*>(bs.data()) == static_cast<const void*>(s.data()));
+            CHECK(bs.length() == s.length_bytes());
         }
     }
 
-    TEST(empty_spans)
-    {
-        {
-            span<int, 0> empty_av(nullptr);
-
-            CHECK(empty_av.bounds().index_bounds() == index<1>{0});
-            CHECK_THROW(empty_av[0], fail_fast);
-            CHECK_THROW(empty_av.begin()[0], fail_fast);
-            CHECK_THROW(empty_av.cbegin()[0], fail_fast);
-            for (auto& v : empty_av) {
-                (void) v;
-                CHECK(false);
-            }
-        }
-
-        {
-            span<int> empty_av = {};
-            CHECK(empty_av.bounds().index_bounds() == index<1>{0});
-            CHECK_THROW(empty_av[0], fail_fast);
-            CHECK_THROW(empty_av.begin()[0], fail_fast);
-            CHECK_THROW(empty_av.cbegin()[0], fail_fast);
-            for (auto& v : empty_av) {
-                (void) v;
-                CHECK(false);
-            }
-        }
-    }
-
-    TEST(index_constructor)
-    {
-        auto arr = new int[8];
-        for (int i = 0; i < 4; ++i) {
-            arr[2 * i] = 4 + i;
-            arr[2 * i + 1] = i;
-        }
-
-        span<int, dynamic_range> av(arr, 8);
-
-        ptrdiff_t a[1] = {0};
-        index<1> i = a;
-
-        CHECK(av[i] == 4);
-
-        auto av2 = as_span(av, dim<4>(), dim<>(2));
-        ptrdiff_t a2[2] = {0, 1};
-        index<2> i2 = a2;
-
-        CHECK(av2[i2] == 0);
-        CHECK(av2[0][i] == 4);
-
-        delete[] arr;
-    }
-
-    TEST(index_constructors)
-    {
-        {
-            // components of the same type
-            index<3> i1(0, 1, 2);
-            CHECK(i1[0] == 0);
-
-            // components of different types
-            size_t c0 = 0;
-            size_t c1 = 1;
-            index<3> i2(c0, c1, 2);
-            CHECK(i2[0] == 0);
-
-            // from array
-            index<3> i3 = {0, 1, 2};
-            CHECK(i3[0] == 0);
-
-            // from other index of the same size type
-            index<3> i4 = i3;
-            CHECK(i4[0] == 0);
-
-            // default
-            index<3> i7;
-            CHECK(i7[0] == 0);
-
-            // default
-            index<3> i9 = {};
-            CHECK(i9[0] == 0);
-        }
-
-        {
-            // components of the same type
-            index<1> i1(0);
-            CHECK(i1[0] == 0);
-
-            // components of different types
-            size_t c0 = 0;
-            index<1> i2(c0);
-            CHECK(i2[0] == 0);
-
-            // from array
-            index<1> i3 = {0};
-            CHECK(i3[0] == 0);
-
-            // from int
-            index<1> i4 = 0;
-            CHECK(i4[0] == 0);
-
-            // from other index of the same size type
-            index<1> i5 = i3;
-            CHECK(i5[0] == 0);
-
-            // default
-            index<1> i8;
-            CHECK(i8[0] == 0);
-
-            // default
-            index<1> i9 = {};
-            CHECK(i9[0] == 0);
-        }
-
-#ifdef CONFIRM_COMPILATION_ERRORS
-        {
-            index<3> i1(0, 1);
-            index<3> i2(0, 1, 2, 3);
-            index<3> i3 = {0};
-            index<3> i4 = {0, 1, 2, 3};
-            index<1> i5 = {0, 1};
-        }
-#endif
-    }
-
-    TEST(index_operations)
-    {
-        ptrdiff_t a[3] = {0, 1, 2};
-        ptrdiff_t b[3] = {3, 4, 5};
-        index<3> i = a;
-        index<3> j = b;
-
-        CHECK(i[0] == 0);
-        CHECK(i[1] == 1);
-        CHECK(i[2] == 2);
-
-        {
-            index<3> k = i + j;
-
-            CHECK(i[0] == 0);
-            CHECK(i[1] == 1);
-            CHECK(i[2] == 2);
-            CHECK(k[0] == 3);
-            CHECK(k[1] == 5);
-            CHECK(k[2] == 7);
-        }
-
-        {
-            index<3> k = i * 3;
-
-            CHECK(i[0] == 0);
-            CHECK(i[1] == 1);
-            CHECK(i[2] == 2);
-            CHECK(k[0] == 0);
-            CHECK(k[1] == 3);
-            CHECK(k[2] == 6);
-        }
-
-        {
-            index<3> k = 3 * i;
-
-            CHECK(i[0] == 0);
-            CHECK(i[1] == 1);
-            CHECK(i[2] == 2);
-            CHECK(k[0] == 0);
-            CHECK(k[1] == 3);
-            CHECK(k[2] == 6);
-        }
-
-        {
-            index<2> k = details::shift_left(i);
-
-            CHECK(i[0] == 0);
-            CHECK(i[1] == 1);
-            CHECK(i[2] == 2);
-            CHECK(k[0] == 1);
-            CHECK(k[1] == 2);
-        }
-    }
-
-    void iterate_second_column(span<int, dynamic_range, dynamic_range> av)
-    {
-        auto length = av.size() / 2;
-
-        // view to the second column
-        auto section = av.section({0, 1}, {length, 1});
-
-        CHECK(section.size() == length);
-        for (auto i = 0; i < section.size(); ++i) {
-            CHECK(section[i][0] == av[i][1]);
-        }
-
-        for (auto i = 0; i < section.size(); ++i) {
-            auto idx = index<2>{i, 0}; // avoid braces inside the CHECK macro
-            CHECK(section[idx] == av[i][1]);
-        }
-
-        CHECK(section.bounds().index_bounds()[0] == length);
-        CHECK(section.bounds().index_bounds()[1] == 1);
-        for (auto i = 0; i < section.bounds().index_bounds()[0]; ++i) {
-            for (auto j = 0; j < section.bounds().index_bounds()[1]; ++j) {
-                auto idx = index<2>{i, j}; // avoid braces inside the CHECK macro
-                CHECK(section[idx] == av[i][1]);
-            }
-        }
-
-        size_t check_sum = 0;
-        for (auto i = 0; i < length; ++i) {
-            check_sum += av[i][1];
-        }
-
-        {
-            auto idx = 0;
-            size_t sum = 0;
-            for (auto num : section) {
-                CHECK(num == av[idx][1]);
-                sum += num;
-                idx++;
-            }
-
-            CHECK(sum == check_sum);
-        }
-        {
-            size_t idx = length - 1;
-            size_t sum = 0;
-            for (auto iter = section.rbegin(); iter != section.rend(); ++iter) {
-                CHECK(*iter == av[idx][1]);
-                sum += *iter;
-                idx--;
-            }
-
-            CHECK(sum == check_sum);
-        }
-    }
-
-    TEST(span_section_iteration)
-    {
-        int arr[4][2] = {{4, 0}, {5, 1}, {6, 2}, {7, 3}};
-
-        // static bounds
-        {
-            span<int, 4, 2> av = arr;
-            iterate_second_column(av);
-        }
-        // first bound is dynamic
-        {
-            span<int, dynamic_range, 2> av = arr;
-            iterate_second_column(av);
-        }
-        // second bound is dynamic
-        {
-            span<int, 4, dynamic_range> av = arr;
-            iterate_second_column(av);
-        }
-        // both bounds are dynamic
-        {
-            span<int, dynamic_range, dynamic_range> av = arr;
-            iterate_second_column(av);
-        }
-    }
-
-    TEST(dynamic_span_section_iteration)
-    {
-        auto height = 4, width = 2;
-        auto size = height * width;
-
-        auto arr = new int[size];
-        for (auto i = 0; i < size; ++i) {
-            arr[i] = i;
-        }
-
-        auto av = as_span(arr, size);
-
-        // first bound is dynamic
-        {
-            span<int, dynamic_range, 2> av2 = as_span(av, dim<>(height), dim<>(width));
-            iterate_second_column(av2);
-        }
-        // second bound is dynamic
-        {
-            span<int, 4, dynamic_range> av2 = as_span(av, dim<>(height), dim<>(width));
-            iterate_second_column(av2);
-        }
-        // both bounds are dynamic
-        {
-            span<int, dynamic_range, dynamic_range> av2 = as_span(av, dim<>(height), dim<>(width));
-            iterate_second_column(av2);
-        }
-
-        delete[] arr;
-    }
-
-    TEST(span_structure_size)
-    {
-        double(*arr)[3][4] = new double[100][3][4];
-        span<double, dynamic_range, 3, 4> av1(arr, 10);
-
-        struct EffectiveStructure
-        {
-            double* v1;
-            ptrdiff_t v2;
-        };
-        CHECK(sizeof(av1) == sizeof(EffectiveStructure));
-
-        CHECK_THROW(av1[10][3][4], fail_fast);
-
-        span<const double, dynamic_range, 6, 4> av2 = as_span(av1, dim<>(5), dim<6>(), dim<4>());
-        (void) av2;
-    }
-
-    TEST(fixed_size_conversions)
-    {
-        int arr[] = {1, 2, 3, 4};
-
-        // converting to an span from an equal size array is ok
-        span<int, 4> av4 = arr;
-        CHECK(av4.length() == 4);
-
-        // converting to dynamic_range a_v is always ok
-        {
-            span<int, dynamic_range> av = av4;
-            (void) av;
-        }
-        {
-            span<int, dynamic_range> av = arr;
-            (void) av;
-        }
-
-// initialization or assignment to static span that REDUCES size is NOT ok
-#ifdef CONFIRM_COMPILATION_ERRORS
-        {
-            span<int, 2> av2 = arr;
-        }
-        {
-            span<int, 2> av2 = av4;
-        }
-#endif
-
-        {
-            span<int, dynamic_range> av = arr;
-            span<int, 2> av2 = av;
-            (void) av2;
-        }
-
-#ifdef CONFIRM_COMPILATION_ERRORS
-        {
-            span<int, dynamic_range> av = arr;
-            span<int, 2, 1> av2 = av.as_span(dim<2>(), dim<2>());
-        }
-#endif
-
-        {
-            span<int, dynamic_range> av = arr;
-            span<int, 2, 1> av2 = as_span(av, dim<>(2), dim<>(2));
-            auto workaround_macro = [&]() { return av2[{1, 0}] == 2; };
-            CHECK(workaround_macro());
-        }
-
-        // but doing so explicitly is ok
-
-        // you can convert statically
-        {
-            span<int, 2> av2 = {arr, 2};
-            (void) av2;
-        }
-        {
-            span<int, 1> av2 = av4.first<1>();
-            (void) av2;
-        }
-
-        // ...or dynamically
-        {
-            // NB: implicit conversion to span<int,2> from span<int,dynamic_range>
-            span<int, 1> av2 = av4.first(1);
-            (void) av2;
-        }
-
-        // initialization or assignment to static span that requires size INCREASE is not ok.
-        int arr2[2] = {1, 2};
-
-#ifdef CONFIRM_COMPILATION_ERRORS
-        {
-            span<int, 4> av4 = arr2;
-        }
-        {
-            span<int, 2> av2 = arr2;
-            span<int, 4> av4 = av2;
-        }
-#endif
-        {
-            auto f = [&]() {
-                span<int, 4> av9 = {arr2, 2};
-                (void) av9;
-            };
-            CHECK_THROW(f(), fail_fast);
-        }
-
-        // this should fail - we are trying to assign a small dynamic a_v to a fixed_size larger one
-        span<int, dynamic_range> av = arr2;
-        auto f = [&]() {
-            span<int, 4> av2 = av;
-            (void) av2;
-        };
-        CHECK_THROW(f(), fail_fast);
-    }
-
     TEST(as_writeable_bytes)
     {
         int a[] = {1, 2, 3, 4};
@@ -1628,51 +1134,114 @@ SUITE(span_tests)
         {
 #ifdef CONFIRM_COMPILATION_ERRORS
             // you should not be able to get writeable bytes for const objects
-            span<const int, dynamic_range> av = a;
-            auto wav = av.as_writeable_bytes();
+            span<const int> s = a;
+            CHECK(s.length() == 4);
+            span<const byte> bs = as_writeable_bytes(s);
+            CHECK(static_cast<void*>(bs.data()) == static_cast<void*>(s.data()));
+            CHECK(bs.length() == s.length_bytes());
 #endif
         }
 
         {
-            span<int, dynamic_range> av;
-            auto wav = as_writeable_bytes(av);
-            CHECK(wav.length() == av.length());
-            CHECK(wav.length() == 0);
-            CHECK(wav.size_bytes() == 0);
+            span<int> s;
+            auto bs = as_writeable_bytes(s);
+            CHECK(bs.length() == s.length());
+            CHECK(bs.length() == 0);
+            CHECK(bs.size_bytes() == 0);
+            CHECK(static_cast<void*>(bs.data()) == static_cast<void*>(s.data()));
+            CHECK(bs.data() == nullptr);
         }
 
         {
-            span<int, dynamic_range> av = a;
-            auto wav = as_writeable_bytes(av);
-            CHECK(wav.data() == (byte*) &a[0]);
-            CHECK(wav.length() == sizeof(a));
+            span<int> s = a;
+            auto bs = as_writeable_bytes(s);
+            CHECK(static_cast<void*>(bs.data()) == static_cast<void*>(s.data()));
+            CHECK(bs.length() == s.length_bytes());
         }
     }
 
-    TEST(iterator)
+    TEST(fixed_size_conversions)
     {
-        int a[] = {1, 2, 3, 4};
+        int arr[] = {1, 2, 3, 4};
 
+        // converting to an span from an equal size array is ok
+        span<int, 4> s4 = arr;
+        CHECK(s4.length() == 4);
+
+        // converting to dynamic_range is always ok
         {
-            span<int, dynamic_range> av = a;
-            auto wav = as_writeable_bytes(av);
-            for (auto& b : wav) {
-                b = byte(0);
-            }
-            for (size_t i = 0; i < 4; ++i) {
-                CHECK(a[i] == 0);
-            }
+            span<int> s = s4;
+            CHECK(s.length() == s4.length());
+            static_cast<void>(s);
         }
 
+// initialization or assignment to static span that REDUCES size is NOT ok
+#ifdef CONFIRM_COMPILATION_ERRORS
         {
-            span<int, dynamic_range> av = a;
-            for (auto& n : av) {
-                n = 1;
-            }
-            for (size_t i = 0; i < 4; ++i) {
-                CHECK(a[i] == 1);
-            }
+            span<int, 2> s = arr;
         }
+        {
+            span<int, 2> s2 = s4;
+            static_cast<void>(s2);
+        }
+#endif
+
+        // even when done dynamically
+        {
+            span<int> s = arr;
+            auto f = [&]() {
+                span<int, 2> s2 = s;
+                static_cast<void>(s2);
+            };
+            CHECK_THROW(f(), fail_fast);
+        }
+
+        // but doing so explicitly is ok
+
+        // you can convert statically
+        {
+            span<int, 2> s2 = {arr, 2};
+            static_cast<void>(s2);
+        }
+        {
+            span<int, 1> s1 = s4.first<1>();
+            static_cast<void>(s1);
+        }
+
+        // ...or dynamically
+        {
+            // NB: implicit conversion to span<int,1> from span<int>
+            span<int, 1> s1 = s4.first(1);
+            static_cast<void>(s1);
+        }
+
+        // initialization or assignment to static span that requires size INCREASE is not ok.
+        int arr2[2] = {1, 2};
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+        {
+            span<int, 4> s3 = arr2;
+        }
+        {
+            span<int, 2> s2 = arr2;
+            span<int, 4> s4a = s2;
+        }
+#endif
+        {
+            auto f = [&]() {
+                span<int, 4> s4 = {arr2, 2};
+                static_cast<void>(s4);
+            };                     
+            CHECK_THROW(f(), fail_fast);
+        }
+
+        // this should fail - we are trying to assign a small dynamic span to a fixed_size larger one
+        span<int> av = arr2;
+        auto f = [&]() {
+            span<int, 4> s4 = av;
+            static_cast<void>(s4);            
+        };
+        CHECK_THROW(f(), fail_fast);
     }
 }
 
diff --git a/tests/strided_span_tests.cpp b/tests/strided_span_tests.cpp
index 0fbf1d7..19056b1 100644
--- a/tests/strided_span_tests.cpp
+++ b/tests/strided_span_tests.cpp
@@ -15,7 +15,7 @@
 ///////////////////////////////////////////////////////////////////////////////
 
 #include <UnitTest++/UnitTest++.h> 
-#include <span.h>
+#include <multi_span.h>
 
 #include <string>
 #include <vector>
@@ -39,7 +39,7 @@ SUITE(strided_span_tests)
 	{
 		int a[30][4][5];
 		
-		auto av = as_span(a);
+		auto av = as_multi_span(a);
 		auto sub = av.section({15, 0, 0}, gsl::index<3>{2, 2, 2});
 		auto subsub = sub.section({1, 0, 0}, gsl::index<3>{1, 1, 1});
 		(void)subsub;
@@ -49,7 +49,7 @@ SUITE(strided_span_tests)
 	{
 		std::vector<int> data(5 * 10);
 		std::iota(begin(data), end(data), 0);
-        const span<int, 5, 10> av = as_span(span<int>{data}, dim<5>(), dim<10>());
+        const multi_span<int, 5, 10> av = as_multi_span(multi_span<int>{data}, dim<5>(), dim<10>());
 
 		strided_span<int, 2> av_section_1 = av.section({ 1, 2 }, { 3, 4 });
 		CHECK((av_section_1[{0, 0}] == 12));
@@ -87,13 +87,13 @@ SUITE(strided_span_tests)
 			CHECK((sav3[{0, 0}] == 1 && sav3[{0, 1}] == 3 && sav3[{1, 0}] == 7));
 		}
 
-		// Check span constructor
+		// Check multi_span constructor
 		{
 			int arr[] = { 1, 2 };
 
 			// From non-cv-qualified source
 			{
-				const span<int> src = arr;
+				const multi_span<int> src = arr;
 
 				strided_span<int, 1> sav{ src, {2, 1} };
 				CHECK(sav.bounds().index_bounds() == index<1>{ 2 });
@@ -102,9 +102,9 @@ SUITE(strided_span_tests)
 
 #if _MSC_VER > 1800
 				//strided_span<const int, 1> sav_c{ {src}, {2, 1} };
-				strided_span<const int, 1> sav_c{ span<const int>{src}, strided_bounds<1>{2, 1} };
+				strided_span<const int, 1> sav_c{ multi_span<const int>{src}, strided_bounds<1>{2, 1} };
 #else
-				strided_span<const int, 1> sav_c{ span<const int>{src}, strided_bounds<1>{2, 1} };
+				strided_span<const int, 1> sav_c{ multi_span<const int>{src}, strided_bounds<1>{2, 1} };
 #endif
 				CHECK(sav_c.bounds().index_bounds() == index<1>{ 2 });
 				CHECK(sav_c.bounds().strides() == index<1>{ 1 });
@@ -113,7 +113,7 @@ SUITE(strided_span_tests)
 #if _MSC_VER > 1800
 				strided_span<volatile int, 1> sav_v{ src, {2, 1} };
 #else
-				strided_span<volatile int, 1> sav_v{ span<volatile int>{src}, strided_bounds<1>{2, 1} };
+				strided_span<volatile int, 1> sav_v{ multi_span<volatile int>{src}, strided_bounds<1>{2, 1} };
 #endif
 				CHECK(sav_v.bounds().index_bounds() == index<1>{ 2 });
 				CHECK(sav_v.bounds().strides() == index<1>{ 1 });
@@ -122,7 +122,7 @@ SUITE(strided_span_tests)
 #if _MSC_VER > 1800
 				strided_span<const volatile int, 1> sav_cv{ src, {2, 1} };
 #else
-				strided_span<const volatile int, 1> sav_cv{ span<const volatile int>{src}, strided_bounds<1>{2, 1} };
+				strided_span<const volatile int, 1> sav_cv{ multi_span<const volatile int>{src}, strided_bounds<1>{2, 1} };
 #endif
 				CHECK(sav_cv.bounds().index_bounds() == index<1>{ 2 });
 				CHECK(sav_cv.bounds().strides() == index<1>{ 1 });
@@ -131,7 +131,7 @@ SUITE(strided_span_tests)
 
 			// From const-qualified source
 			{
-				const span<const int> src{ arr };
+				const multi_span<const int> src{ arr };
 
 				strided_span<const int, 1> sav_c{ src, {2, 1} };
 				CHECK(sav_c.bounds().index_bounds() == index<1>{ 2 });
@@ -141,7 +141,7 @@ SUITE(strided_span_tests)
 #if _MSC_VER > 1800
 				strided_span<const volatile int, 1> sav_cv{ src, {2, 1} };
 #else
-				strided_span<const volatile int, 1> sav_cv{ span<const volatile int>{src}, strided_bounds<1>{2, 1} };
+				strided_span<const volatile int, 1> sav_cv{ multi_span<const volatile int>{src}, strided_bounds<1>{2, 1} };
 #endif
 				
 				CHECK(sav_cv.bounds().index_bounds() == index<1>{ 2 });
@@ -151,7 +151,7 @@ SUITE(strided_span_tests)
 
 			// From volatile-qualified source
 			{
-				const span<volatile int> src{ arr };
+				const multi_span<volatile int> src{ arr };
 
 				strided_span<volatile int, 1> sav_v{ src, {2, 1} };
 				CHECK(sav_v.bounds().index_bounds() == index<1>{ 2 });
@@ -161,7 +161,7 @@ SUITE(strided_span_tests)
 #if _MSC_VER > 1800
 				strided_span<const volatile int, 1> sav_cv{ src, {2, 1} };
 #else
-				strided_span<const volatile int, 1> sav_cv{ span<const volatile int>{src}, strided_bounds<1>{2, 1} };
+				strided_span<const volatile int, 1> sav_cv{ multi_span<const volatile int>{src}, strided_bounds<1>{2, 1} };
 #endif
 				CHECK(sav_cv.bounds().index_bounds() == index<1>{ 2 });
 				CHECK(sav_cv.bounds().strides() == index<1>{ 1 });
@@ -170,7 +170,7 @@ SUITE(strided_span_tests)
 
 			// From cv-qualified source
 			{
-				const span<const volatile int> src{ arr };
+				const multi_span<const volatile int> src{ arr };
 
 				strided_span<const volatile int, 1> sav_cv{ src, {2, 1} };
 				CHECK(sav_cv.bounds().index_bounds() == index<1>{ 2 });
@@ -183,11 +183,11 @@ SUITE(strided_span_tests)
 		{
 			int arr[2] = { 4, 5 };
 
-			const span<int, 2> av(arr, 2);
-			span<const int, 2> av2{ av };
+			const multi_span<int, 2> av(arr, 2);
+			multi_span<const int, 2> av2{ av };
 			CHECK(av2[1] == 5);
 
-			static_assert(std::is_convertible<const span<int, 2>, span<const int, 2>>::value, "ctor is not implicit!");
+			static_assert(std::is_convertible<const multi_span<int, 2>, multi_span<const int, 2>>::value, "ctor is not implicit!");
 		
 			const strided_span<int, 1> src{ arr, {2, 1} };
 			strided_span<const int, 1> sav{ src };
@@ -258,13 +258,13 @@ SUITE(strided_span_tests)
 	{
 		std::vector<int> data(5 * 10);
 		std::iota(begin(data), end(data), 0);
-        const span<int, 5, 10> src = as_span(span<int>{data}, dim<5>(), dim<10>());
+        const multi_span<int, 5, 10> src = as_multi_span(multi_span<int>{data}, dim<5>(), dim<10>());
 
 		const strided_span<int, 2> sav{ src, {{5, 10}, {10, 1}} };
 #ifdef CONFIRM_COMPILATION_ERRORS
 		const strided_span<const int, 2> csav{ {src},{ { 5, 10 },{ 10, 1 } } };
 #endif
-		const strided_span<const int, 2> csav{ span<const int, 5, 10>{ src }, { { 5, 10 },{ 10, 1 } } };
+		const strided_span<const int, 2> csav{ multi_span<const int, 5, 10>{ src }, { { 5, 10 },{ 10, 1 } } };
 
 		strided_span<int, 1> sav_sl = sav[2];
 		CHECK(sav_sl[0] == 20);
@@ -317,7 +317,7 @@ SUITE(strided_span_tests)
 	TEST(strided_span_bounds)
 	{
 		int arr[] = { 0, 1, 2, 3 };
-		span<int> av(arr);
+		multi_span<int> av(arr);
 
 		{
 			// incorrect sections
@@ -413,18 +413,18 @@ SUITE(strided_span_tests)
 			strided_span<int, 1> sav2{ arr, { 1,1,1 } };
 			strided_span<int, 1> sav3{ av, { 1 } };
 			strided_span<int, 1> sav4{ av, { 1,1,1 } };
-			strided_span<int, 2> sav5{ av.as_span(dim<2>(), dim<2>()), { 1 } };
-			strided_span<int, 2> sav6{ av.as_span(dim<2>(), dim<2>()), { 1,1,1 } };
-			strided_span<int, 2> sav7{ av.as_span(dim<2>(), dim<2>()), { { 1,1 },{ 1,1 },{ 1,1 } } };
+			strided_span<int, 2> sav5{ av.as_multi_span(dim<2>(), dim<2>()), { 1 } };
+			strided_span<int, 2> sav6{ av.as_multi_span(dim<2>(), dim<2>()), { 1,1,1 } };
+			strided_span<int, 2> sav7{ av.as_multi_span(dim<2>(), dim<2>()), { { 1,1 },{ 1,1 },{ 1,1 } } };
 
 			index<1> index{ 0, 1 };
 			strided_span<int, 1> sav8{ arr,{ 1,{ 1,1 } } };
 			strided_span<int, 1> sav9{ arr,{ { 1,1 },{ 1,1 } } };
 			strided_span<int, 1> sav10{ av,{ 1,{ 1,1 } } };
 			strided_span<int, 1> sav11{ av,{ { 1,1 },{ 1,1 } } };
-			strided_span<int, 2> sav12{ av.as_span(dim<2>(), dim<2>()),{ { 1 },{ 1 } } };
-			strided_span<int, 2> sav13{ av.as_span(dim<2>(), dim<2>()),{ { 1 },{ 1,1,1 } } };
-			strided_span<int, 2> sav14{ av.as_span(dim<2>(), dim<2>()),{ { 1,1,1 },{ 1 } } };
+			strided_span<int, 2> sav12{ av.as_multi_span(dim<2>(), dim<2>()),{ { 1 },{ 1 } } };
+			strided_span<int, 2> sav13{ av.as_multi_span(dim<2>(), dim<2>()),{ { 1 },{ 1,1,1 } } };
+			strided_span<int, 2> sav14{ av.as_multi_span(dim<2>(), dim<2>()),{ { 1,1,1 },{ 1 } } };
 		}
 #endif
 	}
@@ -432,7 +432,7 @@ SUITE(strided_span_tests)
 	TEST(strided_span_type_conversion)
 	{
 		int arr[] = { 0, 1, 2, 3 };
-		span<int> av(arr);
+		multi_span<int> av(arr);
 
 		{
 			strided_span<int, 1> sav{ av.data(), av.size(), { av.size() / 2, 2 } };
@@ -447,7 +447,7 @@ SUITE(strided_span_tests)
 #endif
 		}
 
-		span<const byte, dynamic_range> bytes = as_bytes(av);
+		multi_span<const byte, dynamic_range> bytes = as_bytes(av);
 
 		// retype strided array with regular strides - from raw data
 		{
@@ -460,10 +460,10 @@ SUITE(strided_span_tests)
 			CHECK_THROW(sav3[0][1], fail_fast);
 		}
 
-		// retype strided array with regular strides - from span
+		// retype strided array with regular strides - from multi_span
 		{
 			strided_bounds<2> bounds{ { 2, bytes.size() / 4 }, { bytes.size() / 2, 1 } };
-			span<const byte, 2, dynamic_range> bytes2 = as_span(bytes, dim<2>(), dim<>(bytes.size() / 2));
+			multi_span<const byte, 2, dynamic_range> bytes2 = as_multi_span(bytes, dim<2>(), dim<>(bytes.size() / 2));
 			strided_span<const byte, 2> sav2{ bytes2, bounds };
 			strided_span<int, 2> sav3 = sav2.as_strided_span<int>();
 			CHECK(sav3[0][0] == 0);
@@ -475,7 +475,7 @@ SUITE(strided_span_tests)
 		// retype strided array with not enough elements - last dimension of the array is too small
 		{
 			strided_bounds<2> bounds{ { 4,2 },{ 4, 1 } };
-			span<const byte, 2, dynamic_range> bytes2 = as_span(bytes, dim<2>(), dim<>(bytes.size() / 2));
+			multi_span<const byte, 2, dynamic_range> bytes2 = as_multi_span(bytes, dim<2>(), dim<>(bytes.size() / 2));
 			strided_span<const byte, 2> sav2{ bytes2, bounds };
 			CHECK_THROW(sav2.as_strided_span<int>(), fail_fast);
 		}
@@ -483,7 +483,7 @@ SUITE(strided_span_tests)
 		// retype strided array with not enough elements - strides are too small
 		{
 			strided_bounds<2> bounds{ { 4,2 },{ 2, 1 } };
-			span<const byte, 2, dynamic_range> bytes2 = as_span(bytes, dim<2>(), dim<>(bytes.size() / 2));
+			multi_span<const byte, 2, dynamic_range> bytes2 = as_multi_span(bytes, dim<2>(), dim<>(bytes.size() / 2));
 			strided_span<const byte, 2> sav2{ bytes2, bounds };
 			CHECK_THROW(sav2.as_strided_span<int>(), fail_fast);
 		}
@@ -491,7 +491,7 @@ SUITE(strided_span_tests)
 		// retype strided array with not enough elements - last dimension does not divide by the new typesize
 		{
 			strided_bounds<2> bounds{ { 2,6 },{ 4, 1 } };
-			span<const byte, 2, dynamic_range> bytes2 = as_span(bytes, dim<2>(), dim<>(bytes.size() / 2));
+			multi_span<const byte, 2, dynamic_range> bytes2 = as_multi_span(bytes, dim<2>(), dim<>(bytes.size() / 2));
 			strided_span<const byte, 2> sav2{ bytes2, bounds };
 			CHECK_THROW(sav2.as_strided_span<int>(), fail_fast);
 		}
@@ -499,7 +499,7 @@ SUITE(strided_span_tests)
 		// retype strided array with not enough elements - strides does not divide by the new typesize
 		{
 			strided_bounds<2> bounds{ { 2, 1 },{ 6, 1 } };
-			span<const byte, 2, dynamic_range> bytes2 = as_span(bytes, dim<2>(), dim<>(bytes.size() / 2));
+			multi_span<const byte, 2, dynamic_range> bytes2 = as_multi_span(bytes, dim<2>(), dim<>(bytes.size() / 2));
 			strided_span<const byte, 2> sav2{ bytes2, bounds };
 			CHECK_THROW(sav2.as_strided_span<int>(), fail_fast);
 		}
@@ -511,7 +511,7 @@ SUITE(strided_span_tests)
 			CHECK_THROW(sav2.as_strided_span<int>(), fail_fast);
 		}
 
-		// retype strided array with irregular strides - from span
+		// retype strided array with irregular strides - from multi_span
 		{
 			strided_bounds<1> bounds{ bytes.size() / 2, 2 };
 			strided_span<const byte, 1> sav2{ bytes, bounds };
@@ -522,7 +522,7 @@ SUITE(strided_span_tests)
 	TEST(empty_strided_spans)
 	{
 		{
-			span<int, 0> empty_av(nullptr);
+			multi_span<int, 0> empty_av(nullptr);
 			strided_span<int, 1> empty_sav{ empty_av, { 0, 1 } };
 
 			CHECK(empty_sav.bounds().index_bounds() == index<1>{ 0 });
@@ -553,7 +553,7 @@ SUITE(strided_span_tests)
 		}
 	}
 
-    void iterate_every_other_element(span<int, dynamic_range> av)
+    void iterate_every_other_element(multi_span<int, dynamic_range> av)
     {
         // pick every other element
 
@@ -586,13 +586,13 @@ SUITE(strided_span_tests)
 
         // static bounds
         {
-            span<int, 8> av(arr, 8);
+            multi_span<int, 8> av(arr, 8);
             iterate_every_other_element(av);
         }
 
         // dynamic bounds
         {
-            span<int, dynamic_range> av(arr, 8);
+            multi_span<int, dynamic_range> av(arr, 8);
             iterate_every_other_element(av);
         }
     }
@@ -606,13 +606,13 @@ SUITE(strided_span_tests)
             arr[2 * i + 1] = i;
         }
 
-        auto av = as_span(arr, 8);
+        auto av = as_multi_span(arr, 8);
         iterate_every_other_element(av);
 
         delete[] arr;
     }
 
-    void iterate_second_slice(span<int, dynamic_range, dynamic_range, dynamic_range> av)
+    void iterate_second_slice(multi_span<int, dynamic_range, dynamic_range, dynamic_range> av)
     {
         int expected[6] = {2,3,10,11,18,19};
         auto section = av.section({0,1,0}, {3,1,2});
@@ -653,7 +653,7 @@ SUITE(strided_span_tests)
         }
 
         {
-            span<int, 3, 4, 2> av = arr;
+            multi_span<int, 3, 4, 2> av = arr;
             iterate_second_slice(av);
         }
     }
@@ -670,22 +670,22 @@ SUITE(strided_span_tests)
         }
 
         {
-            auto av = as_span(as_span(arr, 24), dim<3>(), dim<4>(), dim<2>());
+            auto av = as_multi_span(as_multi_span(arr, 24), dim<3>(), dim<4>(), dim<2>());
             iterate_second_slice(av);
         }
 
         {
-            auto av = as_span(as_span(arr, 24), dim<>(3), dim<4>(), dim<2>());
+            auto av = as_multi_span(as_multi_span(arr, 24), dim<>(3), dim<4>(), dim<2>());
             iterate_second_slice(av);
         }
 
         {
-            auto av = as_span(as_span(arr, 24), dim<3>(), dim<>(4), dim<2>());
+            auto av = as_multi_span(as_multi_span(arr, 24), dim<3>(), dim<>(4), dim<2>());
             iterate_second_slice(av);
         }
 
         {
-            auto av = as_span(as_span(arr, 24), dim<3>(), dim<4>(), dim<>(2));
+            auto av = as_multi_span(as_multi_span(arr, 24), dim<3>(), dim<4>(), dim<>(2));
             iterate_second_slice(av);
         }
         delete[] arr;
@@ -693,7 +693,7 @@ SUITE(strided_span_tests)
 
     TEST(strided_span_conversion)
     {
-        // get an span of 'c' values from the list of X's
+        // get an multi_span of 'c' values from the list of X's
 
         struct X { int a; int b; int c; };
 
@@ -704,7 +704,7 @@ SUITE(strided_span_tests)
         auto d1 = sizeof(int) * 12 / d2;
 
         // convert to 4x12 array of bytes
-        auto av = as_span(as_bytes(as_span(arr, 4)), dim<>(d1), dim<>(d2));
+        auto av = as_multi_span(as_bytes(as_multi_span(arr, 4)), dim<>(d1), dim<>(d2));
 
         CHECK(av.bounds().index_bounds()[0] == 4);
         CHECK(av.bounds().index_bounds()[1] == 12);
diff --git a/tests/string_span_tests.cpp b/tests/string_span_tests.cpp
index 28d7353..876886a 100644
--- a/tests/string_span_tests.cpp
+++ b/tests/string_span_tests.cpp
@@ -40,14 +40,14 @@ SUITE(string_span_tests)
     {
         std::string s = "Hello there world";
         cstring_span<> v = s;
-        CHECK(v.length() == static_cast<cstring_span<>::size_type>(s.length()));
+        CHECK(v.length() == static_cast<cstring_span<>::index_type>(s.length()));
     }
 
     TEST(TestConstructFromStdVector)
     {
         std::vector<char> vec(5, 'h');
-        string_span<> v = vec;
-        CHECK(v.length() == static_cast<string_span<>::size_type>(vec.size()));
+        string_span<> v {vec};
+        CHECK(v.length() == static_cast<string_span<>::index_type>(vec.size()));
     }
 
     TEST(TestStackArrayConstruction)
@@ -109,7 +109,7 @@ SUITE(string_span_tests)
         char stack_string[] = "Hello";
         cstring_span<> v = ensure_z(stack_string);
         auto s2 = gsl::to_string(v);
-        CHECK(static_cast<cstring_span<>::size_type>(s2.length()) == v.length());
+        CHECK(static_cast<cstring_span<>::index_type>(s2.length()) == v.length());
         CHECK(s2.length() == 5);
     }
 
@@ -746,7 +746,7 @@ SUITE(string_span_tests)
     T create() { return T{}; }
 
     template <class T>
-    void use(basic_string_span<T, gsl::dynamic_range> s) {}
+    void use(basic_string_span<T, gsl::dynamic_extent> s) {}
 
     TEST(MoveConstructors)
     {
diff --git a/tests/utils_tests.cpp b/tests/utils_tests.cpp
index a46d6e4..11582de 100644
--- a/tests/utils_tests.cpp
+++ b/tests/utils_tests.cpp
@@ -103,7 +103,7 @@ SUITE(utils_tests)
 
         CHECK(narrow<uint32_t>(int32_t(0)) == 0);
         CHECK(narrow<uint32_t>(int32_t(1)) == 1);
-        CHECK(narrow<uint32_t>(int32_max) == int32_max);
+        CHECK(narrow<uint32_t>(int32_max) == static_cast<uint32_t>(int32_max));
 
         CHECK_THROW(narrow<uint32_t>(int32_t(-1)), narrowing_error);
         CHECK_THROW(narrow<uint32_t>(int32_min), narrowing_error);