diff --git a/include/gsl/span b/include/gsl/span
index 566f731..c011d76 100644
--- a/include/gsl/span
+++ b/include/gsl/span
@@ -403,9 +403,7 @@ public:
     using difference_type = std::ptrdiff_t;
 
     using iterator = details::span_iterator<ElementType>;
-    using const_iterator = details::span_iterator<const ElementType>;
     using reverse_iterator = std::reverse_iterator<iterator>;
-    using const_reverse_iterator = std::reverse_iterator<const_iterator>;
 
 #if defined(GSL_USE_STATIC_CONSTEXPR_WORKAROUND)
     static constexpr const size_type extent{Extent};
@@ -594,31 +592,9 @@ public:
         return {data, endData, endData};
     }
 
-    constexpr const_iterator cbegin() const noexcept
-    {
-        const auto data = storage_.data();
-        return {data, data + size(), data};
-    }
-
-    constexpr const_iterator cend() const noexcept
-    {
-        const auto data = storage_.data();
-        const auto endData = data + storage_.size();
-        return {data, endData, endData};
-    }
-
     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()};
-    }
-
 #ifdef _MSC_VER
     // Tell MSVC how to unwrap spans in range-based-for
     constexpr pointer _Unchecked_begin() const noexcept { return data(); }
diff --git a/include/gsl/span_ext b/include/gsl/span_ext
index b466df8..1d375fd 100644
--- a/include/gsl/span_ext
+++ b/include/gsl/span_ext
@@ -1,198 +1,198 @@
-///////////////////////////////////////////////////////////////////////////////
-//
-// 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.
-//
-///////////////////////////////////////////////////////////////////////////////
-
-#ifndef GSL_SPAN_EXT_H
-#define GSL_SPAN_EXT_H
-
-///////////////////////////////////////////////////////////////////////////////
-//
-// File: span_ext
-// Purpose: continue offering features that have been cut from the official
-//   implementation of span.
-//   While modernizing gsl::span a number of features needed to be removed to
-//   be compliant with the design of std::span
-//
-///////////////////////////////////////////////////////////////////////////////
-
-
-#include <gsl/gsl_util> // for narrow_cast, narrow
-#include <gsl/span>     // for span
-
-#include <algorithm> // for lexicographical_compare
-#include <cstddef>   // for ptrdiff_t, size_t
-#include <utility>
-
-namespace gsl
-{
-
-// [span.comparison], span comparison operators
-template <class ElementType, std::size_t FirstExtent, std::size_t SecondExtent>
-constexpr bool operator==(span<ElementType, FirstExtent> l, span<ElementType, SecondExtent> r)
-{
-    return std::equal(l.begin(), l.end(), r.begin(), r.end());
-}
-
-template <class ElementType, std::size_t Extent>
-constexpr bool operator!=(span<ElementType, Extent> l, span<ElementType, Extent> r)
-{
-    return !(l == r);
-}
-
-template <class ElementType, std::size_t Extent>
-constexpr bool operator<(span<ElementType, Extent> l, span<ElementType, Extent> r)
-{
-    return std::lexicographical_compare(l.begin(), l.end(), r.begin(), r.end());
-}
-
-template <class ElementType, std::size_t Extent>
-constexpr bool operator<=(span<ElementType, Extent> l, span<ElementType, Extent> r)
-{
-    return !(l > r);
-}
-
-template <class ElementType, std::size_t Extent>
-constexpr bool operator>(span<ElementType, Extent> l, span<ElementType, Extent> r)
-{
-    return r < l;
-}
-
-template <class ElementType, std::size_t Extent>
-constexpr bool operator>=(span<ElementType, Extent> l, span<ElementType, Extent> r)
-{
-    return !(l < r);
-}
-
-//
-// make_span() - Utility functions for creating spans
-//
-template <class ElementType>
-constexpr span<ElementType> make_span(ElementType* ptr, typename span<ElementType>::size_type count)
-{
-    return span<ElementType>(ptr, count);
-}
-
-template <class ElementType>
-constexpr span<ElementType> make_span(ElementType* firstElem, ElementType* lastElem)
-{
-    return span<ElementType>(firstElem, lastElem);
-}
-
-template <class ElementType, std::size_t N>
-constexpr span<ElementType, N> make_span(ElementType (&arr)[N]) noexcept
-{
-    return span<ElementType, N>(arr);
-}
-
-template <class Container>
-constexpr span<typename Container::value_type> make_span(Container& cont)
-{
-    return span<typename Container::value_type>(cont);
-}
-
-template <class Container>
-constexpr span<const typename Container::value_type> make_span(const Container& cont)
-{
-    return span<const typename Container::value_type>(cont);
-}
-
-template <class Ptr>
-constexpr span<typename Ptr::element_type> make_span(Ptr& cont, std::size_t count)
-{
-    return span<typename Ptr::element_type>(cont, count);
-}
-
-template <class Ptr>
-constexpr span<typename Ptr::element_type> make_span(Ptr& cont)
-{
-    return span<typename Ptr::element_type>(cont);
-}
-
-// Specialization of gsl::at for span
-template <class ElementType, std::size_t Extent>
-constexpr ElementType& at(span<ElementType, Extent> s, index i)
-{
-    // No bounds checking here because it is done in span::operator[] called below
-    Ensures(i >= 0);
-    return s[narrow_cast<std::size_t>(i)];
-}
-
-// [span.obs] Free observer functions
-template <class ElementType, std::size_t Extent>
-constexpr std::ptrdiff_t ssize(const span<ElementType, Extent>& s) noexcept
-{
-    return static_cast<std::ptrdiff_t>(s.size());
-}
-
-// [span.iter] Free functions for begin/end functions
-template <class ElementType, std::size_t Extent>
-constexpr typename span<ElementType, Extent>::iterator
-begin(const span<ElementType, Extent>& s) noexcept
-{
-    return s.begin();
-}
-
-template <class ElementType, std::size_t Extent = dynamic_extent>
-constexpr typename span<ElementType, Extent>::iterator
-end(const span<ElementType, Extent>& s) noexcept
-{
-    return s.end();
-}
-
-template <class ElementType, std::size_t Extent>
-constexpr typename span<ElementType, Extent>::const_iterator
-cbegin(const span<ElementType, Extent>& s) noexcept
-{
-    return s.cbegin();
-}
-
-template <class ElementType, std::size_t Extent>
-constexpr typename span<ElementType, Extent>::const_iterator
-cend(const span<ElementType, Extent>& s) noexcept
-{
-    return s.cend();
-}
-
-template <class ElementType, std::size_t Extent>
-constexpr typename span<ElementType, Extent>::reverse_iterator
-rbegin(const span<ElementType, Extent>& s) noexcept
-{
-    return s.rbegin();
-}
-
-template <class ElementType, std::size_t Extent>
-constexpr typename span<ElementType, Extent>::reverse_iterator
-rend(const span<ElementType, Extent>& s) noexcept
-{
-    return s.rend();
-}
-
-template <class ElementType, std::size_t Extent>
-constexpr typename span<ElementType, Extent>::const_reverse_iterator
-crbegin(const span<ElementType, Extent>& s) noexcept
-{
-    return s.crbegin();
-}
-
-template <class ElementType, std::size_t Extent>
-constexpr typename span<ElementType, Extent>::const_reverse_iterator
-crend(const span<ElementType, Extent>& s) noexcept
-{
-    return s.crend();
-}
-
-} // namespace gsl
-
-#endif // GSL_SPAN_EXT_H
+///////////////////////////////////////////////////////////////////////////////
+//
+// 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.
+//
+///////////////////////////////////////////////////////////////////////////////
+
+#ifndef GSL_SPAN_EXT_H
+#define GSL_SPAN_EXT_H
+
+///////////////////////////////////////////////////////////////////////////////
+//
+// File: span_ext
+// Purpose: continue offering features that have been cut from the official
+//   implementation of span.
+//   While modernizing gsl::span a number of features needed to be removed to
+//   be compliant with the design of std::span
+//
+///////////////////////////////////////////////////////////////////////////////
+
+
+#include <gsl/gsl_util> // for narrow_cast, narrow
+#include <gsl/span>     // for span
+
+#include <algorithm> // for lexicographical_compare
+#include <cstddef>   // for ptrdiff_t, size_t
+#include <utility>
+
+namespace gsl
+{
+
+// [span.comparison], span comparison operators
+template <class ElementType, std::size_t FirstExtent, std::size_t SecondExtent>
+constexpr bool operator==(span<ElementType, FirstExtent> l, span<ElementType, SecondExtent> r)
+{
+    return std::equal(l.begin(), l.end(), r.begin(), r.end());
+}
+
+template <class ElementType, std::size_t Extent>
+constexpr bool operator!=(span<ElementType, Extent> l, span<ElementType, Extent> r)
+{
+    return !(l == r);
+}
+
+template <class ElementType, std::size_t Extent>
+constexpr bool operator<(span<ElementType, Extent> l, span<ElementType, Extent> r)
+{
+    return std::lexicographical_compare(l.begin(), l.end(), r.begin(), r.end());
+}
+
+template <class ElementType, std::size_t Extent>
+constexpr bool operator<=(span<ElementType, Extent> l, span<ElementType, Extent> r)
+{
+    return !(l > r);
+}
+
+template <class ElementType, std::size_t Extent>
+constexpr bool operator>(span<ElementType, Extent> l, span<ElementType, Extent> r)
+{
+    return r < l;
+}
+
+template <class ElementType, std::size_t Extent>
+constexpr bool operator>=(span<ElementType, Extent> l, span<ElementType, Extent> r)
+{
+    return !(l < r);
+}
+
+//
+// make_span() - Utility functions for creating spans
+//
+template <class ElementType>
+constexpr span<ElementType> make_span(ElementType* ptr, typename span<ElementType>::size_type count)
+{
+    return span<ElementType>(ptr, count);
+}
+
+template <class ElementType>
+constexpr span<ElementType> make_span(ElementType* firstElem, ElementType* lastElem)
+{
+    return span<ElementType>(firstElem, lastElem);
+}
+
+template <class ElementType, std::size_t N>
+constexpr span<ElementType, N> make_span(ElementType (&arr)[N]) noexcept
+{
+    return span<ElementType, N>(arr);
+}
+
+template <class Container>
+constexpr span<typename Container::value_type> make_span(Container& cont)
+{
+    return span<typename Container::value_type>(cont);
+}
+
+template <class Container>
+constexpr span<const typename Container::value_type> make_span(const Container& cont)
+{
+    return span<const typename Container::value_type>(cont);
+}
+
+template <class Ptr>
+constexpr span<typename Ptr::element_type> make_span(Ptr& cont, std::size_t count)
+{
+    return span<typename Ptr::element_type>(cont, count);
+}
+
+template <class Ptr>
+constexpr span<typename Ptr::element_type> make_span(Ptr& cont)
+{
+    return span<typename Ptr::element_type>(cont);
+}
+
+// Specialization of gsl::at for span
+template <class ElementType, std::size_t Extent>
+constexpr ElementType& at(span<ElementType, Extent> s, index i)
+{
+    // No bounds checking here because it is done in span::operator[] called below
+    Ensures(i >= 0);
+    return s[narrow_cast<std::size_t>(i)];
+}
+
+// [span.obs] Free observer functions
+template <class ElementType, std::size_t Extent>
+constexpr std::ptrdiff_t ssize(const span<ElementType, Extent>& s) noexcept
+{
+    return static_cast<std::ptrdiff_t>(s.size());
+}
+
+// [span.iter] Free functions for begin/end functions
+template <class ElementType, std::size_t Extent>
+constexpr typename span<ElementType, Extent>::iterator
+begin(const span<ElementType, Extent>& s) noexcept
+{
+    return s.begin();
+}
+
+template <class ElementType, std::size_t Extent = dynamic_extent>
+constexpr typename span<ElementType, Extent>::iterator
+end(const span<ElementType, Extent>& s) noexcept
+{
+    return s.end();
+}
+
+template <class ElementType, std::size_t Extent>
+constexpr typename span<ElementType, Extent>::reverse_iterator
+rbegin(const span<ElementType, Extent>& s) noexcept
+{
+    return s.rbegin();
+}
+
+template <class ElementType, std::size_t Extent>
+constexpr typename span<ElementType, Extent>::reverse_iterator
+rend(const span<ElementType, Extent>& s) noexcept
+{
+    return s.rend();
+}
+
+template <class ElementType, std::size_t Extent>
+constexpr typename span<ElementType, Extent>::iterator
+cbegin(const span<ElementType, Extent>& s) noexcept
+{
+    return s.begin();
+}
+
+template <class ElementType, std::size_t Extent = dynamic_extent>
+constexpr typename span<ElementType, Extent>::iterator
+cend(const span<ElementType, Extent>& s) noexcept
+{
+    return s.end();
+}
+
+template <class ElementType, std::size_t Extent>
+constexpr typename span<ElementType, Extent>::reverse_iterator
+crbegin(const span<ElementType, Extent>& s) noexcept
+{
+    return s.rbegin();
+}
+
+template <class ElementType, std::size_t Extent>
+constexpr typename span<ElementType, Extent>::reverse_iterator
+crend(const span<ElementType, Extent>& s) noexcept
+{
+    return s.rend();
+}
+
+} // namespace gsl
+
+#endif // GSL_SPAN_EXT_H
diff --git a/include/gsl/string_span b/include/gsl/string_span
index 2207291..b96c9ff 100644
--- a/include/gsl/string_span
+++ b/include/gsl/string_span
@@ -1,724 +1,716 @@
-///////////////////////////////////////////////////////////////////////////////
-//
-// 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.
-//
-///////////////////////////////////////////////////////////////////////////////
-
-#ifndef GSL_STRING_SPAN_H
-#define GSL_STRING_SPAN_H
-
-#include <gsl/gsl_assert> // for Ensures, Expects
-#include <gsl/gsl_util>   // for narrow_cast
-#include <gsl/span_ext>       // for operator!=, operator==, dynamic_extent
-
-#include <algorithm> // for equal, lexicographical_compare
-#include <array>     // for array
-#include <cstddef>   // for size_t, nullptr_t
-#include <cstdint>   // for PTRDIFF_MAX
-#include <cstring>
-#include <string>    // for basic_string, allocator, char_traits
-#include <type_traits> // for declval, is_convertible, enable_if_t, add_...
-
-#if defined(_MSC_VER) && !defined(__clang__)
-#pragma warning(push)
-
-// Turn MSVC /analyze rules that generate too much noise. TODO: fix in the tool.
-#pragma warning(disable : 26446) // TODO: bug in parser - attributes and templates
-#pragma warning(disable : 26481) // TODO: suppress does not work inside templates sometimes
-
-#if _MSC_VER < 1910
-#pragma push_macro("constexpr")
-#define constexpr /*constexpr*/
-
-#endif // _MSC_VER < 1910
-#endif // _MSC_VER
-
-namespace gsl
-{
-//
-// czstring and wzstring
-//
-// These are "tag" typedefs for C-style strings (i.e. null-terminated character arrays)
-// that allow static analysis to help find bugs.
-//
-// There are no additional features/semantics that we can find a way to add inside the
-// type system for these types that will not either incur significant runtime costs or
-// (sometimes needlessly) break existing programs when introduced.
-//
-
-template <typename CharT, std::size_t Extent = dynamic_extent>
-using basic_zstring = CharT*;
-
-template <std::size_t Extent = dynamic_extent>
-using czstring = basic_zstring<const char, Extent>;
-
-template <std::size_t Extent = dynamic_extent>
-using cwzstring = basic_zstring<const wchar_t, Extent>;
-
-template <std::size_t Extent = dynamic_extent>
-using cu16zstring = basic_zstring<const char16_t, Extent>;
-
-template <std::size_t Extent = dynamic_extent>
-using cu32zstring = basic_zstring<const char32_t, Extent>;
-
-template <std::size_t Extent = dynamic_extent>
-using zstring = basic_zstring<char, Extent>;
-
-template <std::size_t Extent = dynamic_extent>
-using wzstring = basic_zstring<wchar_t, Extent>;
-
-template <std::size_t Extent = dynamic_extent>
-using u16zstring = basic_zstring<char16_t, Extent>;
-
-template <std::size_t Extent = dynamic_extent>
-using u32zstring = basic_zstring<char32_t, Extent>;
-
-namespace details
-{
-    template <class CharT>
-    std::size_t string_length(const CharT* str, std::size_t n)
-    {
-        if (str == nullptr || n == dynamic_extent) return 0;
-
-        const span<const CharT> str_span{str, n};
-
-        std::size_t len = 0;
-        while (len < n && str_span[len]) len++;
-
-        return len;
-    }
-} // namespace details
-
-//
-// ensure_sentinel()
-//
-// Provides a way to obtain an span from a contiguous sequence
-// that ends with a (non-inclusive) sentinel value.
-//
-// Will fail-fast if sentinel cannot be found before max elements are examined.
-//
-template <typename T, const T Sentinel>
-span<T, dynamic_extent> ensure_sentinel(T* seq,
-                                        std::size_t max = static_cast<std::size_t>(-1))
-{
-    Ensures(seq != nullptr);
-
-    GSL_SUPPRESS(
-        f.23) // NO-FORMAT: attribute // TODO: false positive // TODO: suppress does not work
-    auto cur = seq;
-    Ensures(cur != nullptr); // workaround for removing the warning
-
-    GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute // TODO: suppress does not work
-    while (static_cast<std::size_t>(cur - seq) < max && *cur != Sentinel) ++cur;
-    Ensures(*cur == Sentinel);
-    return {seq, static_cast<std::size_t>(cur - seq)};
-}
-
-//
-// ensure_z - creates a span for a zero terminated strings.
-// Will fail fast if a null-terminator cannot be found before
-// the limit of size_type.
-//
-template <typename CharT>
-span<CharT, dynamic_extent> ensure_z(CharT* const& sz,
-                                     std::size_t max = static_cast<std::size_t>(-1))
-{
-    return ensure_sentinel<CharT, CharT(0)>(sz, max);
-}
-
-template <typename CharT, std::size_t N>
-span<CharT, dynamic_extent> ensure_z(CharT (&sz)[N])
-{
-    return ensure_z(&sz[0], N);
-}
-
-template <class Cont>
-span<typename std::remove_pointer<typename Cont::pointer>::type, dynamic_extent>
-ensure_z(Cont& cont)
-{
-    return ensure_z(cont.data(), cont.size());
-}
-
-template <typename CharT, std::size_t>
-class basic_string_span;
-
-namespace details
-{
-    template <typename T>
-    struct is_basic_string_span_oracle : std::false_type
-    {
-    };
-
-    template <typename CharT, std::size_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>>
-    {
-    };
-} // namespace details
-
-//
-// string_span and relatives
-//
-template <typename CharT, std::size_t Extent = dynamic_extent>
-class basic_string_span
-{
-public:
-    using element_type = CharT;
-    using value_type = std::remove_cv_t<element_type>;
-    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 = typename impl_type::size_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() noexcept = default;
-
-    // copy
-    constexpr basic_string_span(const basic_string_span& other) noexcept = default;
-
-    // assign
-    constexpr basic_string_span& operator=(const basic_string_span& other) noexcept = default;
-
-    constexpr basic_string_span(pointer ptr, size_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 <std::size_t N>
-    constexpr basic_string_span(element_type (&arr)[N]) : span_(remove_z(arr))
-    {}
-
-    template <std::size_t N, class ArrayElementType = std::remove_const_t<element_type>>
-    constexpr basic_string_span(std::array<ArrayElementType, N>& arr) noexcept : span_(arr)
-    {}
-
-    template <std::size_t N, class ArrayElementType = std::remove_const_t<element_type>>
-    constexpr basic_string_span(const std::array<ArrayElementType, N>& arr) noexcept : span_(arr)
-    {}
-
-    // Container signature should work for basic_string after C++17 version exists
-    template <class Traits, class Allocator>
-    // GSL_SUPPRESS(bounds.4) // NO-FORMAT: attribute // TODO: parser bug
-    constexpr basic_string_span(std::basic_string<element_type, Traits, Allocator>& str)
-        : span_(&str[0], str.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 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)
-    {}
-
-    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 <
-        class OtherValueType, std::size_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())
-    {}
-
-    template <size_type Count>
-    constexpr basic_string_span<element_type, Count> first() const
-    {
-        return {span_.template first<Count>()};
-    }
-
-    constexpr basic_string_span<element_type, dynamic_extent> first(size_type count) const
-    {
-        return {span_.first(count)};
-    }
-
-    template <size_type Count>
-    constexpr basic_string_span<element_type, Count> last() const
-    {
-        return {span_.template last<Count>()};
-    }
-
-    constexpr basic_string_span<element_type, dynamic_extent> last(size_type count) const
-    {
-        return {span_.last(count)};
-    }
-
-    template <size_type Offset, size_type Count>
-    constexpr basic_string_span<element_type, Count> subspan() const
-    {
-        return {span_.template subspan<Offset, Count>()};
-    }
-
-    constexpr basic_string_span<element_type, dynamic_extent>
-    subspan(size_type offset, size_type count = dynamic_extent) const
-    {
-        return {span_.subspan(offset, count)};
-    }
-
-    constexpr reference operator[](size_type idx) const { return span_[idx]; }
-    constexpr reference operator()(size_type idx) const { return span_[idx]; }
-
-    constexpr pointer data() const { return span_.data(); }
-
-    constexpr size_type length() const noexcept { return span_.size(); }
-    constexpr size_type size() const noexcept { return span_.size(); }
-    constexpr size_type size_bytes() const noexcept { return span_.size_bytes(); }
-    constexpr size_type length_bytes() const noexcept { return span_.length_bytes(); }
-    constexpr bool empty() const noexcept { return size() == 0; }
-
-    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(); }
-
-private:
-    static impl_type remove_z(pointer const& sz, std::size_t max)
-    {
-        return {sz, details::string_length(sz, max)};
-    }
-
-    template <std::size_t N>
-    static impl_type remove_z(element_type (&sz)[N])
-    {
-        return remove_z(&sz[0], N);
-    }
-
-    impl_type span_;
-};
-
-template <std::size_t Extent = dynamic_extent>
-using string_span = basic_string_span<char, Extent>;
-
-template <std::size_t Extent = dynamic_extent>
-using cstring_span = basic_string_span<const char, Extent>;
-
-template <std::size_t Extent = dynamic_extent>
-using wstring_span = basic_string_span<wchar_t, Extent>;
-
-template <std::size_t Extent = dynamic_extent>
-using cwstring_span = basic_string_span<const wchar_t, Extent>;
-
-template <std::size_t Extent = dynamic_extent>
-using u16string_span = basic_string_span<char16_t, Extent>;
-
-template <std::size_t Extent = dynamic_extent>
-using cu16string_span = basic_string_span<const char16_t, Extent>;
-
-template <std::size_t Extent = dynamic_extent>
-using u32string_span = basic_string_span<char32_t, Extent>;
-
-template <std::size_t Extent = dynamic_extent>
-using cu32string_span = basic_string_span<const char32_t, Extent>;
-
-//
-// to_string() allow (explicit) conversions from string_span to string
-//
-
-template <typename CharT, std::size_t Extent>
-std::basic_string<typename std::remove_const<CharT>::type>
-to_string(basic_string_span<CharT, Extent> view)
-{
-    return {view.data(), narrow_cast<std::size_t>(view.length())};
-}
-
-template <typename CharT, typename Traits = typename std::char_traits<CharT>,
-          typename Allocator = std::allocator<CharT>, typename gCharT, std::size_t Extent>
-std::basic_string<CharT, Traits, Allocator> to_basic_string(basic_string_span<gCharT, Extent> view)
-{
-    return {view.data(), narrow_cast<std::size_t>(view.length())};
-}
-
-template <class ElementType, std::size_t Extent>
-basic_string_span<const byte, details::calculate_byte_size<ElementType, Extent>::value>
-as_bytes(basic_string_span<ElementType, Extent> s) noexcept
-{
-    GSL_SUPPRESS(type.1) // NO-FORMAT: attribute
-    return {reinterpret_cast<const byte*>(s.data()), s.size_bytes()};
-}
-
-template <class ElementType, std::size_t Extent,
-          class = std::enable_if_t<!std::is_const<ElementType>::value>>
-basic_string_span<byte, details::calculate_byte_size<ElementType, Extent>::value>
-as_writable_bytes(basic_string_span<ElementType, Extent> s) noexcept
-{
-    GSL_SUPPRESS(type.1) // NO-FORMAT: attribute
-    return {reinterpret_cast<byte*>(s.data()), s.size_bytes()};
-}
-
-// zero-terminated string span, used to convert
-// zero-terminated spans to legacy strings
-template <typename CharT, std::size_t Extent = dynamic_extent>
-class basic_zstring_span
-{
-public:
-    using value_type = CharT;
-    using const_value_type = std::add_const_t<CharT>;
-
-    using pointer = std::add_pointer_t<value_type>;
-    using const_pointer = std::add_pointer_t<const_value_type>;
-
-    using zstring_type = basic_zstring<value_type, Extent>;
-    using const_zstring_type = basic_zstring<const_value_type, Extent>;
-
-    using impl_type = span<value_type, Extent>;
-    using string_span_type = basic_string_span<value_type, Extent>;
-
-    constexpr basic_zstring_span(impl_type s) : span_(s)
-    {
-        // expects a zero-terminated span
-        Expects(s[s.size() - 1] == '\0');
-    }
-
-    // copy
-    constexpr basic_zstring_span(const basic_zstring_span& other) = default;
-
-    // move
-    constexpr basic_zstring_span(basic_zstring_span&& other) = default;
-
-    // assign
-    constexpr basic_zstring_span& operator=(const basic_zstring_span& other) = default;
-
-    // move assign
-    constexpr basic_zstring_span& operator=(basic_zstring_span&& other) = default;
-
-    constexpr bool empty() const noexcept { return span_.size() == 0; }
-
-    constexpr string_span_type as_string_span() const noexcept
-    {
-        const auto sz = span_.size();
-        return {span_.data(), sz > 1 ? sz - 1 : 0};
-    }
-    constexpr string_span_type ensure_z() const { return gsl::ensure_z(span_); }
-
-    constexpr const_zstring_type assume_z() const noexcept { return span_.data(); }
-
-private:
-    impl_type span_;
-};
-
-template <std::size_t Max = dynamic_extent>
-using zstring_span = basic_zstring_span<char, Max>;
-
-template <std::size_t Max = dynamic_extent>
-using wzstring_span = basic_zstring_span<wchar_t, Max>;
-
-template <std::size_t Max = dynamic_extent>
-using u16zstring_span = basic_zstring_span<char16_t, Max>;
-
-template <std::size_t Max = dynamic_extent>
-using u32zstring_span = basic_zstring_span<char32_t, Max>;
-
-template <std::size_t Max = dynamic_extent>
-using czstring_span = basic_zstring_span<const char, Max>;
-
-template <std::size_t Max = dynamic_extent>
-using cwzstring_span = basic_zstring_span<const wchar_t, Max>;
-
-template <std::size_t Max = dynamic_extent>
-using cu16zstring_span = basic_zstring_span<const char16_t, Max>;
-
-template <std::size_t Max = dynamic_extent>
-using cu32zstring_span = basic_zstring_span<const char32_t, Max>;
-
-// operator ==
-template <class CharT, std::size_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)
-{
-    const gsl::basic_string_span<std::add_const_t<CharT>> tmp(other);
-    return std::equal(one.begin(), one.end(), tmp.begin(), tmp.end());
-}
-
-template <class CharT, std::size_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)
-{
-    const gsl::basic_string_span<std::add_const_t<CharT>> tmp(one);
-    return std::equal(tmp.begin(), tmp.end(), other.begin(), other.end());
-}
-
-// operator !=
-template <typename CharT, std::size_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)
-{
-    return !(one == other);
-}
-
-template <
-    typename CharT, std::size_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 &&
-        !gsl::details::is_basic_string_span<T>::value>>
-bool operator!=(const T& one, gsl::basic_string_span<CharT, Extent> other)
-{
-    return !(one == other);
-}
-
-// operator<
-template <typename CharT, std::size_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)
-{
-    const 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::size_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 &&
-        !gsl::details::is_basic_string_span<T>::value>>
-bool operator<(const T& one, gsl::basic_string_span<CharT, Extent> other)
-{
-    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
-
-// 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::size_t Extent = gsl::dynamic_extent, typename T,
-    typename DataType = typename T::value_type,
-    typename = 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)
-{
-    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::size_t Extent = gsl::dynamic_extent, typename T,
-    typename DataType = typename T::value_type,
-    typename = 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)
-{
-    gsl::basic_string_span<std::add_const_t<CharT>, Extent> tmp(one);
-    return std::lexicographical_compare(tmp.begin(), tmp.end(), other.begin(), other.end());
-}
-#endif
-
-// operator <=
-template <typename CharT, std::size_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)
-{
-    return !(other < one);
-}
-
-template <
-    typename CharT, std::size_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 &&
-        !gsl::details::is_basic_string_span<T>::value>>
-bool operator<=(const T& one, gsl::basic_string_span<CharT, Extent> other)
-{
-    return !(other < one);
-}
-
-#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::size_t Extent = gsl::dynamic_extent, typename T,
-    typename DataType = typename T::value_type,
-    typename = 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)
-{
-    return !(other < one);
-}
-
-template <
-    typename CharT, std::size_t Extent = gsl::dynamic_extent, typename T,
-    typename DataType = typename T::value_type,
-    typename = 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)
-{
-    return !(other < one);
-}
-#endif
-
-// operator>
-template <typename CharT, std::size_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)
-{
-    return other < one;
-}
-
-template <
-    typename CharT, std::size_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 &&
-        !gsl::details::is_basic_string_span<T>::value>>
-bool operator>(const T& one, gsl::basic_string_span<CharT, Extent> other)
-{
-    return other < one;
-}
-
-#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::size_t Extent = gsl::dynamic_extent, typename T,
-    typename DataType = typename T::value_type,
-    typename = 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)
-{
-    return other < one;
-}
-
-template <
-    typename CharT, std::size_t Extent = gsl::dynamic_extent, typename T,
-    typename DataType = typename T::value_type,
-    typename = 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)
-{
-    return other < one;
-}
-#endif
-
-// operator >=
-template <typename CharT, std::size_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)
-{
-    return !(one < other);
-}
-
-template <
-    typename CharT, std::size_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 &&
-        !gsl::details::is_basic_string_span<T>::value>>
-bool operator>=(const T& one, gsl::basic_string_span<CharT, Extent> other)
-{
-    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::size_t Extent = gsl::dynamic_extent, typename T,
-    typename DataType = typename T::value_type,
-    typename = 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)
-{
-    return !(one < other);
-}
-
-template <
-    typename CharT, std::size_t Extent = gsl::dynamic_extent, typename T,
-    typename DataType = typename T::value_type,
-    typename = 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)
-{
-    return !(one < other);
-}
-#endif
-} // namespace gsl
-
-#if defined(_MSC_VER) && !defined(__clang__)
-#pragma warning(pop)
-
-#if _MSC_VER < 1910
-#undef constexpr
-#pragma pop_macro("constexpr")
-
-#endif // _MSC_VER < 1910
-#endif // _MSC_VER
-
-#endif // GSL_STRING_SPAN_H
+///////////////////////////////////////////////////////////////////////////////
+//
+// 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.
+//
+///////////////////////////////////////////////////////////////////////////////
+
+#ifndef GSL_STRING_SPAN_H
+#define GSL_STRING_SPAN_H
+
+#include <gsl/gsl_assert> // for Ensures, Expects
+#include <gsl/gsl_util>   // for narrow_cast
+#include <gsl/span_ext>       // for operator!=, operator==, dynamic_extent
+
+#include <algorithm> // for equal, lexicographical_compare
+#include <array>     // for array
+#include <cstddef>   // for size_t, nullptr_t
+#include <cstdint>   // for PTRDIFF_MAX
+#include <cstring>
+#include <string>    // for basic_string, allocator, char_traits
+#include <type_traits> // for declval, is_convertible, enable_if_t, add_...
+
+#if defined(_MSC_VER) && !defined(__clang__)
+#pragma warning(push)
+
+// Turn MSVC /analyze rules that generate too much noise. TODO: fix in the tool.
+#pragma warning(disable : 26446) // TODO: bug in parser - attributes and templates
+#pragma warning(disable : 26481) // TODO: suppress does not work inside templates sometimes
+
+#if _MSC_VER < 1910
+#pragma push_macro("constexpr")
+#define constexpr /*constexpr*/
+
+#endif // _MSC_VER < 1910
+#endif // _MSC_VER
+
+namespace gsl
+{
+//
+// czstring and wzstring
+//
+// These are "tag" typedefs for C-style strings (i.e. null-terminated character arrays)
+// that allow static analysis to help find bugs.
+//
+// There are no additional features/semantics that we can find a way to add inside the
+// type system for these types that will not either incur significant runtime costs or
+// (sometimes needlessly) break existing programs when introduced.
+//
+
+template <typename CharT, std::size_t Extent = dynamic_extent>
+using basic_zstring = CharT*;
+
+template <std::size_t Extent = dynamic_extent>
+using czstring = basic_zstring<const char, Extent>;
+
+template <std::size_t Extent = dynamic_extent>
+using cwzstring = basic_zstring<const wchar_t, Extent>;
+
+template <std::size_t Extent = dynamic_extent>
+using cu16zstring = basic_zstring<const char16_t, Extent>;
+
+template <std::size_t Extent = dynamic_extent>
+using cu32zstring = basic_zstring<const char32_t, Extent>;
+
+template <std::size_t Extent = dynamic_extent>
+using zstring = basic_zstring<char, Extent>;
+
+template <std::size_t Extent = dynamic_extent>
+using wzstring = basic_zstring<wchar_t, Extent>;
+
+template <std::size_t Extent = dynamic_extent>
+using u16zstring = basic_zstring<char16_t, Extent>;
+
+template <std::size_t Extent = dynamic_extent>
+using u32zstring = basic_zstring<char32_t, Extent>;
+
+namespace details
+{
+    template <class CharT>
+    std::size_t string_length(const CharT* str, std::size_t n)
+    {
+        if (str == nullptr || n == dynamic_extent) return 0;
+
+        const span<const CharT> str_span{str, n};
+
+        std::size_t len = 0;
+        while (len < n && str_span[len]) len++;
+
+        return len;
+    }
+} // namespace details
+
+//
+// ensure_sentinel()
+//
+// Provides a way to obtain an span from a contiguous sequence
+// that ends with a (non-inclusive) sentinel value.
+//
+// Will fail-fast if sentinel cannot be found before max elements are examined.
+//
+template <typename T, const T Sentinel>
+span<T, dynamic_extent> ensure_sentinel(T* seq,
+                                        std::size_t max = static_cast<std::size_t>(-1))
+{
+    Ensures(seq != nullptr);
+
+    GSL_SUPPRESS(
+        f.23) // NO-FORMAT: attribute // TODO: false positive // TODO: suppress does not work
+    auto cur = seq;
+    Ensures(cur != nullptr); // workaround for removing the warning
+
+    GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute // TODO: suppress does not work
+    while (static_cast<std::size_t>(cur - seq) < max && *cur != Sentinel) ++cur;
+    Ensures(*cur == Sentinel);
+    return {seq, static_cast<std::size_t>(cur - seq)};
+}
+
+//
+// ensure_z - creates a span for a zero terminated strings.
+// Will fail fast if a null-terminator cannot be found before
+// the limit of size_type.
+//
+template <typename CharT>
+span<CharT, dynamic_extent> ensure_z(CharT* const& sz,
+                                     std::size_t max = static_cast<std::size_t>(-1))
+{
+    return ensure_sentinel<CharT, CharT(0)>(sz, max);
+}
+
+template <typename CharT, std::size_t N>
+span<CharT, dynamic_extent> ensure_z(CharT (&sz)[N])
+{
+    return ensure_z(&sz[0], N);
+}
+
+template <class Cont>
+span<typename std::remove_pointer<typename Cont::pointer>::type, dynamic_extent>
+ensure_z(Cont& cont)
+{
+    return ensure_z(cont.data(), cont.size());
+}
+
+template <typename CharT, std::size_t>
+class basic_string_span;
+
+namespace details
+{
+    template <typename T>
+    struct is_basic_string_span_oracle : std::false_type
+    {
+    };
+
+    template <typename CharT, std::size_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>>
+    {
+    };
+} // namespace details
+
+//
+// string_span and relatives
+//
+template <typename CharT, std::size_t Extent = dynamic_extent>
+class basic_string_span
+{
+public:
+    using element_type = CharT;
+    using value_type = std::remove_cv_t<element_type>;
+    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 = typename impl_type::size_type;
+    using iterator = typename impl_type::iterator;
+    using reverse_iterator = typename impl_type::reverse_iterator;
+
+    // default (empty)
+    constexpr basic_string_span() noexcept = default;
+
+    // copy
+    constexpr basic_string_span(const basic_string_span& other) noexcept = default;
+
+    // assign
+    constexpr basic_string_span& operator=(const basic_string_span& other) noexcept = default;
+
+    constexpr basic_string_span(pointer ptr, size_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 <std::size_t N>
+    constexpr basic_string_span(element_type (&arr)[N]) : span_(remove_z(arr))
+    {}
+
+    template <std::size_t N, class ArrayElementType = std::remove_const_t<element_type>>
+    constexpr basic_string_span(std::array<ArrayElementType, N>& arr) noexcept : span_(arr)
+    {}
+
+    template <std::size_t N, class ArrayElementType = std::remove_const_t<element_type>>
+    constexpr basic_string_span(const std::array<ArrayElementType, N>& arr) noexcept : span_(arr)
+    {}
+
+    // Container signature should work for basic_string after C++17 version exists
+    template <class Traits, class Allocator>
+    // GSL_SUPPRESS(bounds.4) // NO-FORMAT: attribute // TODO: parser bug
+    constexpr basic_string_span(std::basic_string<element_type, Traits, Allocator>& str)
+        : span_(&str[0], str.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 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)
+    {}
+
+    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 <
+        class OtherValueType, std::size_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())
+    {}
+
+    template <size_type Count>
+    constexpr basic_string_span<element_type, Count> first() const
+    {
+        return {span_.template first<Count>()};
+    }
+
+    constexpr basic_string_span<element_type, dynamic_extent> first(size_type count) const
+    {
+        return {span_.first(count)};
+    }
+
+    template <size_type Count>
+    constexpr basic_string_span<element_type, Count> last() const
+    {
+        return {span_.template last<Count>()};
+    }
+
+    constexpr basic_string_span<element_type, dynamic_extent> last(size_type count) const
+    {
+        return {span_.last(count)};
+    }
+
+    template <size_type Offset, size_type Count>
+    constexpr basic_string_span<element_type, Count> subspan() const
+    {
+        return {span_.template subspan<Offset, Count>()};
+    }
+
+    constexpr basic_string_span<element_type, dynamic_extent>
+    subspan(size_type offset, size_type count = dynamic_extent) const
+    {
+        return {span_.subspan(offset, count)};
+    }
+
+    constexpr reference operator[](size_type idx) const { return span_[idx]; }
+    constexpr reference operator()(size_type idx) const { return span_[idx]; }
+
+    constexpr pointer data() const { return span_.data(); }
+
+    constexpr size_type length() const noexcept { return span_.size(); }
+    constexpr size_type size() const noexcept { return span_.size(); }
+    constexpr size_type size_bytes() const noexcept { return span_.size_bytes(); }
+    constexpr size_type length_bytes() const noexcept { return span_.length_bytes(); }
+    constexpr bool empty() const noexcept { return size() == 0; }
+
+    constexpr iterator begin() const noexcept { return span_.begin(); }
+    constexpr iterator end() const noexcept { return span_.end(); }
+
+    constexpr reverse_iterator rbegin() const noexcept { return span_.rbegin(); }
+    constexpr reverse_iterator rend() const noexcept { return span_.rend(); }
+
+private:
+    static impl_type remove_z(pointer const& sz, std::size_t max)
+    {
+        return {sz, details::string_length(sz, max)};
+    }
+
+    template <std::size_t N>
+    static impl_type remove_z(element_type (&sz)[N])
+    {
+        return remove_z(&sz[0], N);
+    }
+
+    impl_type span_;
+};
+
+template <std::size_t Extent = dynamic_extent>
+using string_span = basic_string_span<char, Extent>;
+
+template <std::size_t Extent = dynamic_extent>
+using cstring_span = basic_string_span<const char, Extent>;
+
+template <std::size_t Extent = dynamic_extent>
+using wstring_span = basic_string_span<wchar_t, Extent>;
+
+template <std::size_t Extent = dynamic_extent>
+using cwstring_span = basic_string_span<const wchar_t, Extent>;
+
+template <std::size_t Extent = dynamic_extent>
+using u16string_span = basic_string_span<char16_t, Extent>;
+
+template <std::size_t Extent = dynamic_extent>
+using cu16string_span = basic_string_span<const char16_t, Extent>;
+
+template <std::size_t Extent = dynamic_extent>
+using u32string_span = basic_string_span<char32_t, Extent>;
+
+template <std::size_t Extent = dynamic_extent>
+using cu32string_span = basic_string_span<const char32_t, Extent>;
+
+//
+// to_string() allow (explicit) conversions from string_span to string
+//
+
+template <typename CharT, std::size_t Extent>
+std::basic_string<typename std::remove_const<CharT>::type>
+to_string(basic_string_span<CharT, Extent> view)
+{
+    return {view.data(), narrow_cast<std::size_t>(view.length())};
+}
+
+template <typename CharT, typename Traits = typename std::char_traits<CharT>,
+          typename Allocator = std::allocator<CharT>, typename gCharT, std::size_t Extent>
+std::basic_string<CharT, Traits, Allocator> to_basic_string(basic_string_span<gCharT, Extent> view)
+{
+    return {view.data(), narrow_cast<std::size_t>(view.length())};
+}
+
+template <class ElementType, std::size_t Extent>
+basic_string_span<const byte, details::calculate_byte_size<ElementType, Extent>::value>
+as_bytes(basic_string_span<ElementType, Extent> s) noexcept
+{
+    GSL_SUPPRESS(type.1) // NO-FORMAT: attribute
+    return {reinterpret_cast<const byte*>(s.data()), s.size_bytes()};
+}
+
+template <class ElementType, std::size_t Extent,
+          class = std::enable_if_t<!std::is_const<ElementType>::value>>
+basic_string_span<byte, details::calculate_byte_size<ElementType, Extent>::value>
+as_writable_bytes(basic_string_span<ElementType, Extent> s) noexcept
+{
+    GSL_SUPPRESS(type.1) // NO-FORMAT: attribute
+    return {reinterpret_cast<byte*>(s.data()), s.size_bytes()};
+}
+
+// zero-terminated string span, used to convert
+// zero-terminated spans to legacy strings
+template <typename CharT, std::size_t Extent = dynamic_extent>
+class basic_zstring_span
+{
+public:
+    using value_type = CharT;
+    using const_value_type = std::add_const_t<CharT>;
+
+    using pointer = std::add_pointer_t<value_type>;
+    using const_pointer = std::add_pointer_t<const_value_type>;
+
+    using zstring_type = basic_zstring<value_type, Extent>;
+    using const_zstring_type = basic_zstring<const_value_type, Extent>;
+
+    using impl_type = span<value_type, Extent>;
+    using string_span_type = basic_string_span<value_type, Extent>;
+
+    constexpr basic_zstring_span(impl_type s) : span_(s)
+    {
+        // expects a zero-terminated span
+        Expects(s[s.size() - 1] == '\0');
+    }
+
+    // copy
+    constexpr basic_zstring_span(const basic_zstring_span& other) = default;
+
+    // move
+    constexpr basic_zstring_span(basic_zstring_span&& other) = default;
+
+    // assign
+    constexpr basic_zstring_span& operator=(const basic_zstring_span& other) = default;
+
+    // move assign
+    constexpr basic_zstring_span& operator=(basic_zstring_span&& other) = default;
+
+    constexpr bool empty() const noexcept { return span_.size() == 0; }
+
+    constexpr string_span_type as_string_span() const noexcept
+    {
+        const auto sz = span_.size();
+        return {span_.data(), sz > 1 ? sz - 1 : 0};
+    }
+    constexpr string_span_type ensure_z() const { return gsl::ensure_z(span_); }
+
+    constexpr const_zstring_type assume_z() const noexcept { return span_.data(); }
+
+private:
+    impl_type span_;
+};
+
+template <std::size_t Max = dynamic_extent>
+using zstring_span = basic_zstring_span<char, Max>;
+
+template <std::size_t Max = dynamic_extent>
+using wzstring_span = basic_zstring_span<wchar_t, Max>;
+
+template <std::size_t Max = dynamic_extent>
+using u16zstring_span = basic_zstring_span<char16_t, Max>;
+
+template <std::size_t Max = dynamic_extent>
+using u32zstring_span = basic_zstring_span<char32_t, Max>;
+
+template <std::size_t Max = dynamic_extent>
+using czstring_span = basic_zstring_span<const char, Max>;
+
+template <std::size_t Max = dynamic_extent>
+using cwzstring_span = basic_zstring_span<const wchar_t, Max>;
+
+template <std::size_t Max = dynamic_extent>
+using cu16zstring_span = basic_zstring_span<const char16_t, Max>;
+
+template <std::size_t Max = dynamic_extent>
+using cu32zstring_span = basic_zstring_span<const char32_t, Max>;
+
+// operator ==
+template <class CharT, std::size_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)
+{
+    const gsl::basic_string_span<std::add_const_t<CharT>> tmp(other);
+    return std::equal(one.begin(), one.end(), tmp.begin(), tmp.end());
+}
+
+template <class CharT, std::size_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)
+{
+    const gsl::basic_string_span<std::add_const_t<CharT>> tmp(one);
+    return std::equal(tmp.begin(), tmp.end(), other.begin(), other.end());
+}
+
+// operator !=
+template <typename CharT, std::size_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)
+{
+    return !(one == other);
+}
+
+template <
+    typename CharT, std::size_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 &&
+        !gsl::details::is_basic_string_span<T>::value>>
+bool operator!=(const T& one, gsl::basic_string_span<CharT, Extent> other)
+{
+    return !(one == other);
+}
+
+// operator<
+template <typename CharT, std::size_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)
+{
+    const 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::size_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 &&
+        !gsl::details::is_basic_string_span<T>::value>>
+bool operator<(const T& one, gsl::basic_string_span<CharT, Extent> other)
+{
+    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
+
+// 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::size_t Extent = gsl::dynamic_extent, typename T,
+    typename DataType = typename T::value_type,
+    typename = 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)
+{
+    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::size_t Extent = gsl::dynamic_extent, typename T,
+    typename DataType = typename T::value_type,
+    typename = 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)
+{
+    gsl::basic_string_span<std::add_const_t<CharT>, Extent> tmp(one);
+    return std::lexicographical_compare(tmp.begin(), tmp.end(), other.begin(), other.end());
+}
+#endif
+
+// operator <=
+template <typename CharT, std::size_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)
+{
+    return !(other < one);
+}
+
+template <
+    typename CharT, std::size_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 &&
+        !gsl::details::is_basic_string_span<T>::value>>
+bool operator<=(const T& one, gsl::basic_string_span<CharT, Extent> other)
+{
+    return !(other < one);
+}
+
+#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::size_t Extent = gsl::dynamic_extent, typename T,
+    typename DataType = typename T::value_type,
+    typename = 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)
+{
+    return !(other < one);
+}
+
+template <
+    typename CharT, std::size_t Extent = gsl::dynamic_extent, typename T,
+    typename DataType = typename T::value_type,
+    typename = 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)
+{
+    return !(other < one);
+}
+#endif
+
+// operator>
+template <typename CharT, std::size_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)
+{
+    return other < one;
+}
+
+template <
+    typename CharT, std::size_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 &&
+        !gsl::details::is_basic_string_span<T>::value>>
+bool operator>(const T& one, gsl::basic_string_span<CharT, Extent> other)
+{
+    return other < one;
+}
+
+#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::size_t Extent = gsl::dynamic_extent, typename T,
+    typename DataType = typename T::value_type,
+    typename = 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)
+{
+    return other < one;
+}
+
+template <
+    typename CharT, std::size_t Extent = gsl::dynamic_extent, typename T,
+    typename DataType = typename T::value_type,
+    typename = 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)
+{
+    return other < one;
+}
+#endif
+
+// operator >=
+template <typename CharT, std::size_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)
+{
+    return !(one < other);
+}
+
+template <
+    typename CharT, std::size_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 &&
+        !gsl::details::is_basic_string_span<T>::value>>
+bool operator>=(const T& one, gsl::basic_string_span<CharT, Extent> other)
+{
+    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::size_t Extent = gsl::dynamic_extent, typename T,
+    typename DataType = typename T::value_type,
+    typename = 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)
+{
+    return !(one < other);
+}
+
+template <
+    typename CharT, std::size_t Extent = gsl::dynamic_extent, typename T,
+    typename DataType = typename T::value_type,
+    typename = 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)
+{
+    return !(one < other);
+}
+#endif
+} // namespace gsl
+
+#if defined(_MSC_VER) && !defined(__clang__)
+#pragma warning(pop)
+
+#if _MSC_VER < 1910
+#undef constexpr
+#pragma pop_macro("constexpr")
+
+#endif // _MSC_VER < 1910
+#endif // _MSC_VER
+
+#endif // GSL_STRING_SPAN_H
diff --git a/tests/span_compatibility_tests.cpp b/tests/span_compatibility_tests.cpp
index ab29748..bebfb77 100644
--- a/tests/span_compatibility_tests.cpp
+++ b/tests/span_compatibility_tests.cpp
@@ -387,12 +387,8 @@ TEST(span_compatibility_tests, assertion_tests)
         static_assert(noexcept(sp_dyn.data()), "noexcept(sp_dyn.data())");
         static_assert(noexcept(sp_dyn.begin()), "noexcept(sp_dyn.begin())");
         static_assert(noexcept(sp_dyn.end()), "noexcept(sp_dyn.end())");
-        static_assert(noexcept(sp_dyn.cbegin()), "noexcept(sp_dyn.cbegin())");
-        static_assert(noexcept(sp_dyn.cend()), "noexcept(sp_dyn.cend())");
         static_assert(noexcept(sp_dyn.rbegin()), "noexcept(sp_dyn.rbegin())");
         static_assert(noexcept(sp_dyn.rend()), "noexcept(sp_dyn.rend())");
-        static_assert(noexcept(sp_dyn.crbegin()), "noexcept(sp_dyn.crbegin())");
-        static_assert(noexcept(sp_dyn.crend()), "noexcept(sp_dyn.crend())");
 
         static_assert(noexcept(sp_nine.size()), "noexcept(sp_nine.size())");
         static_assert(noexcept(sp_nine.size_bytes()), "noexcept(sp_nine.size_bytes())");
@@ -403,12 +399,8 @@ TEST(span_compatibility_tests, assertion_tests)
         static_assert(noexcept(sp_nine.data()), "noexcept(sp_nine.data())");
         static_assert(noexcept(sp_nine.begin()), "noexcept(sp_nine.begin())");
         static_assert(noexcept(sp_nine.end()), "noexcept(sp_nine.end())");
-        static_assert(noexcept(sp_nine.cbegin()), "noexcept(sp_nine.cbegin())");
-        static_assert(noexcept(sp_nine.cend()), "noexcept(sp_nine.cend())");
         static_assert(noexcept(sp_nine.rbegin()), "noexcept(sp_nine.rbegin())");
         static_assert(noexcept(sp_nine.rend()), "noexcept(sp_nine.rend())");
-        static_assert(noexcept(sp_nine.crbegin()), "noexcept(sp_nine.crbegin())");
-        static_assert(noexcept(sp_nine.crend()), "noexcept(sp_nine.crend())");
 
         EXPECT_TRUE(sp_dyn.size() == 9);
         EXPECT_TRUE(sp_nine.size() == 9);
@@ -446,24 +438,12 @@ TEST(span_compatibility_tests, assertion_tests)
         EXPECT_TRUE(sp_dyn.end()[-2] == 80);
         EXPECT_TRUE(sp_nine.end()[-2] == 80);
 
-        EXPECT_TRUE(*sp_dyn.cbegin() == 10);
-        EXPECT_TRUE(*sp_nine.cbegin() == 10);
-
-        EXPECT_TRUE(sp_dyn.cend()[-2] == 80);
-        EXPECT_TRUE(sp_nine.cend()[-2] == 80);
-
         EXPECT_TRUE(*sp_dyn.rbegin() == 90);
         EXPECT_TRUE(*sp_nine.rbegin() == 90);
 
         EXPECT_TRUE(sp_dyn.rend()[-2] == 20);
         EXPECT_TRUE(sp_nine.rend()[-2] == 20);
 
-        EXPECT_TRUE(*sp_dyn.crbegin() == 90);
-        EXPECT_TRUE(*sp_nine.crbegin() == 90);
-
-        EXPECT_TRUE(sp_dyn.crend()[-2] == 20);
-        EXPECT_TRUE(sp_nine.crend()[-2] == 20);
-
         static_assert(is_same<decltype(sp_dyn.begin()), gsl::span<int>::iterator>::value,
                       "is_same<decltype(sp_dyn.begin()), gsl::span<int>::iterator>::value");
         static_assert(is_same<decltype(sp_nine.begin()), gsl::span<int, 9>::iterator>::value,
@@ -472,16 +452,6 @@ TEST(span_compatibility_tests, assertion_tests)
                       "is_same<decltype(sp_dyn.end()), gsl::span<int>::iterator>::value");
         static_assert(is_same<decltype(sp_nine.end()), gsl::span<int, 9>::iterator>::value,
                       "is_same<decltype(sp_nine.end()), gsl::span<int, 9>::iterator>::value");
-        static_assert(is_same<decltype(sp_dyn.cbegin()), gsl::span<int>::const_iterator>::value,
-                      "is_same<decltype(sp_dyn.cbegin()), gsl::span<int>::const_iterator>::value");
-        static_assert(
-            is_same<decltype(sp_nine.cbegin()), gsl::span<int, 9>::const_iterator>::value,
-            "is_same<decltype(sp_nine.cbegin()), gsl::span<int, 9>::const_iterator>::value");
-        static_assert(is_same<decltype(sp_dyn.cend()), gsl::span<int>::const_iterator>::value,
-                      "is_same<decltype(sp_dyn.cend()), gsl::span<int>::const_iterator>::value");
-        static_assert(
-            is_same<decltype(sp_nine.cend()), gsl::span<int, 9>::const_iterator>::value,
-            "is_same<decltype(sp_nine.cend()), gsl::span<int, 9>::const_iterator>::value");
         static_assert(
             is_same<decltype(sp_dyn.rbegin()), gsl::span<int>::reverse_iterator>::value,
             "is_same<decltype(sp_dyn.rbegin()), gsl::span<int>::reverse_iterator>::value");
@@ -493,19 +463,6 @@ TEST(span_compatibility_tests, assertion_tests)
         static_assert(
             is_same<decltype(sp_nine.rend()), gsl::span<int, 9>::reverse_iterator>::value,
             "is_same<decltype(sp_nine.rend()), gsl::span<int, 9>::reverse_iterator>::value");
-        static_assert(
-            is_same<decltype(sp_dyn.crbegin()), gsl::span<int>::const_reverse_iterator>::value,
-            "is_same<decltype(sp_dyn.crbegin()), gsl::span<int>::const_reverse_iterator>::value");
-        static_assert(
-            is_same<decltype(sp_nine.crbegin()), gsl::span<int, 9>::const_reverse_iterator>::value,
-            "is_same<decltype(sp_nine.crbegin()), gsl::span<int, "
-            "9>::const_reverse_iterator>::value");
-        static_assert(
-            is_same<decltype(sp_dyn.crend()), gsl::span<int>::const_reverse_iterator>::value,
-            "is_same<decltype(sp_dyn.crend()), gsl::span<int>::const_reverse_iterator>::value");
-        static_assert(
-            is_same<decltype(sp_nine.crend()), gsl::span<int, 9>::const_reverse_iterator>::value,
-            "is_same<decltype(sp_nine.crend()), gsl::span<int, 9>::const_reverse_iterator>::value");
     }
     {
         int sequence[9]{10, 20, 30, 40, 50, 60, 70, 80, 90};
@@ -646,90 +603,54 @@ static_assert(std::is_same<gsl::span<const int, 3>::const_reference, const int&>
 // assertions for span_iterator
 static_assert(std::is_same<std::iterator_traits<gsl::span<int>::iterator>::pointer, int*>::value,
               "span<int>::iterator's pointer should be int*");
-static_assert(
-    std::is_same<std::iterator_traits<gsl::span<int>::const_iterator>::pointer, const int*>::value,
-    "span<int>::const_iterator's pointer should be const int*");
 static_assert(
     std::is_same<gsl::span<int>::reverse_iterator,
                  std::reverse_iterator<gsl::span<int>::iterator>>::value,
     "span<int>::reverse_iterator should equal std::reverse_iterator<span<int>::iterator>");
-static_assert(std::is_same<gsl::span<int>::const_reverse_iterator,
-                           std::reverse_iterator<gsl::span<int>::const_iterator>>::value,
-              "span<int>::const_reverse_iterator should equal "
-              "std::reverse_iterator<span<int>::const_iterator>");
 
 static_assert(std::is_same<std::iterator_traits<gsl::span<int, 3>::iterator>::pointer, int*>::value,
               "span<int, 3>::iterator's pointer should be int*");
-static_assert(std::is_same<std::iterator_traits<gsl::span<int, 3>::const_iterator>::pointer,
-                           const int*>::value,
-              "span<int, 3>::const_iterator's pointer should be const int*");
 static_assert(
     std::is_same<gsl::span<int, 3>::reverse_iterator,
                  std::reverse_iterator<gsl::span<int, 3>::iterator>>::value,
     "span<int, 3>::reverse_iterator should equal std::reverse_iterator<span<int, 3>::iterator>");
-static_assert(std::is_same<gsl::span<int, 3>::const_reverse_iterator,
-                           std::reverse_iterator<gsl::span<int, 3>::const_iterator>>::value,
-              "span<int, 3>::const_reverse_iterator should equal std::reverse_iterator<span<int, "
-              "3>::const_iterator>");
 
 static_assert(
     std::is_same<std::iterator_traits<gsl::span<const int>::iterator>::pointer, const int*>::value,
     "span<const int>::iterator's pointer should be int*");
-static_assert(std::is_same<std::iterator_traits<gsl::span<const int>::const_iterator>::pointer,
-                           const int*>::value,
-              "span<const int>::const_iterator's pointer should be const int*");
 static_assert(std::is_same<gsl::span<const int>::reverse_iterator,
                            std::reverse_iterator<gsl::span<const int>::iterator>>::value,
               "span<const int>::reverse_iterator should equal std::reverse_iterator<span<const "
               "int>::iterator>");
-static_assert(std::is_same<gsl::span<const int>::const_reverse_iterator,
-                           std::reverse_iterator<gsl::span<const int>::const_iterator>>::value,
-              "span<const int>::const_reverse_iterator should equal "
-              "std::reverse_iterator<span<const int>::const_iterator>");
 
 static_assert(std::is_same<std::iterator_traits<gsl::span<const int, 3>::iterator>::pointer,
                            const int*>::value,
               "span<const int, 3>::iterator's pointer should be int*");
-static_assert(std::is_same<std::iterator_traits<gsl::span<const int, 3>::const_iterator>::pointer,
-                           const int*>::value,
-              "span<const int, 3>::const_iterator's pointer should be const int*");
 static_assert(std::is_same<gsl::span<const int, 3>::reverse_iterator,
                            std::reverse_iterator<gsl::span<const int, 3>::iterator>>::value,
               "span<const int, 3>::reverse_iterator should equal std::reverse_iterator<span<const "
               "int, 3>::iterator>");
-static_assert(std::is_same<gsl::span<const int, 3>::const_reverse_iterator,
-                           std::reverse_iterator<gsl::span<const int, 3>::const_iterator>>::value,
-              "span<const int, 3>::const_reverse_iterator should equal "
-              "std::reverse_iterator<span<const int, 3>::const_iterator>");
 
 // copyability assertions
 static_assert(std::is_trivially_copyable<gsl::span<int>>::value,
               "span<int> should be trivially copyable");
 static_assert(std::is_trivially_copyable<gsl::span<int>::iterator>::value,
               "span<int>::iterator should be trivially copyable");
-static_assert(std::is_trivially_copyable<gsl::span<int>::const_iterator>::value,
-              "span<int>::const_iterator should be trivially copyable");
 
 static_assert(std::is_trivially_copyable<gsl::span<int, 3>>::value,
               "span<int, 3> should be trivially copyable");
 static_assert(std::is_trivially_copyable<gsl::span<int, 3>::iterator>::value,
               "span<int, 3>::iterator should be trivially copyable");
-static_assert(std::is_trivially_copyable<gsl::span<int, 3>::const_iterator>::value,
-              "span<int, 3>::const_iterator should be trivially copyable");
 
 static_assert(std::is_trivially_copyable<gsl::span<const int>>::value,
               "span<const int> should be trivially copyable");
 static_assert(std::is_trivially_copyable<gsl::span<const int>::iterator>::value,
               "span<const int>::iterator should be trivially copyable");
-static_assert(std::is_trivially_copyable<gsl::span<const int>::const_iterator>::value,
-              "span<const int>::const_iterator should be trivially copyable");
 
 static_assert(std::is_trivially_copyable<gsl::span<const int, 3>>::value,
               "span<const int, 3> should be trivially copyable");
 static_assert(std::is_trivially_copyable<gsl::span<const int, 3>::iterator>::value,
               "span<const int, 3>::iterator should be trivially copyable");
-static_assert(std::is_trivially_copyable<gsl::span<const int, 3>::const_iterator>::value,
-              "span<const int, 3>::const_iterator should be trivially copyable");
 
 // nothrow constructible assertions
 static_assert(std::is_nothrow_constructible<gsl::span<int>, int*, std::size_t>::value,
diff --git a/tests/span_ext_tests.cpp b/tests/span_ext_tests.cpp
index bd256a8..d413e03 100644
--- a/tests/span_ext_tests.cpp
+++ b/tests/span_ext_tests.cpp
@@ -1,360 +1,360 @@
-///////////////////////////////////////////////////////////////////////////////
-//
-// 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 <gtest/gtest.h>
-
-#include <gsl/gsl_util> // for narrow_cast, at
-#include <gsl/span_ext> // for operator==, operator!=, make_span
-
-#include <array>       // for array
-#include <iostream>    // for cerr
-#include <vector>      // for vector
-
-using namespace std;
-using namespace gsl;
-
-namespace
-{
-static constexpr char deathstring[] = "Expected Death";
-} // namespace
-
-TEST(span_ext_test, make_span_from_pointer_length_constructor)
-{
-    std::set_terminate([] {
-        std::cerr << "Expected Death. from_pointer_length_constructor";
-        std::abort();
-    });
-    int arr[4] = {1, 2, 3, 4};
-
-    {
-        auto s = make_span(&arr[0], 2);
-        EXPECT_TRUE(s.size() == 2);
-        EXPECT_TRUE(s.data() == &arr[0]);
-        EXPECT_TRUE(s[0] == 1);
-        EXPECT_TRUE(s[1] == 2);
-    }
-
-    {
-        int* p = nullptr;
-        auto s = make_span(p, narrow_cast<span<int>::size_type>(0));
-        EXPECT_TRUE(s.size() == 0);
-        EXPECT_TRUE(s.data() == nullptr);
-    }
-
-    {
-        int* p = nullptr;
-        auto workaround_macro = [=]() { make_span(p, 2); };
-        EXPECT_DEATH(workaround_macro(), deathstring);
-    }
-}
-
-TEST(span_ext_test, make_span_from_pointer_pointer_construction)
-{
-    int arr[4] = {1, 2, 3, 4};
-
-    {
-        auto s = make_span(&arr[0], &arr[2]);
-        EXPECT_TRUE(s.size() == 2);
-        EXPECT_TRUE(s.data() == &arr[0]);
-        EXPECT_TRUE(s[0] == 1);
-        EXPECT_TRUE(s[1] == 2);
-    }
-
-    {
-        auto s = make_span(&arr[0], &arr[0]);
-        EXPECT_TRUE(s.size() == 0);
-        EXPECT_TRUE(s.data() == &arr[0]);
-    }
-
-    {
-        int* p = nullptr;
-        auto s = make_span(p, p);
-        EXPECT_TRUE(s.size() == 0);
-        EXPECT_TRUE(s.data() == nullptr);
-    }
-}
-
-TEST(span_ext_test, make_span_from_array_constructor)
- {
-     int arr[5] = {1, 2, 3, 4, 5};
-     int arr2d[2][3] = {1, 2, 3, 4, 5, 6};
-     int arr3d[2][3][2] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12};
-
-     {
-         const auto s = make_span(arr);
-         EXPECT_TRUE(s.size() == 5);
-         EXPECT_TRUE(s.data() == std::addressof(arr[0]));
-     }
-
-     {
-         const auto s = make_span(std::addressof(arr2d[0]), 1);
-         EXPECT_TRUE(s.size() == 1);
-         EXPECT_TRUE(s.data() == std::addressof(arr2d[0]));
-     }
-
-     {
-         const auto s = make_span(std::addressof(arr3d[0]), 1);
-         EXPECT_TRUE(s.size() == 1);
-         EXPECT_TRUE(s.data() == std::addressof(arr3d[0]));
-     }
- }
-
- TEST(span_ext_test, make_span_from_dynamic_array_constructor)
- {
-     double(*arr)[3][4] = new double[100][3][4];
-
-     {
-         auto s = make_span(&arr[0][0][0], 10);
-         EXPECT_TRUE(s.size() == 10);
-         EXPECT_TRUE(s.data() == &arr[0][0][0]);
-     }
-
-     delete[] arr;
- }
-
- TEST(span_ext_test, make_span_from_std_array_constructor)
- {
-     std::array<int, 4> arr = {1, 2, 3, 4};
-
-     {
-         auto s = make_span(arr);
-         EXPECT_TRUE(s.size() == arr.size());
-         EXPECT_TRUE(s.data() == arr.data());
-     }
-
-     // This test checks for the bug found in gcc 6.1, 6.2, 6.3, 6.4, 6.5 7.1, 7.2, 7.3 - issue #590
-     {
-         span<int> s1 = make_span(arr);
-
-         static span<int> s2;
-         s2 = s1;
-
- #if defined(__GNUC__) && __GNUC__ == 6 && (__GNUC_MINOR__ == 4 || __GNUC_MINOR__ == 5) &&          \
-     __GNUC_PATCHLEVEL__ == 0 && defined(__OPTIMIZE__)
-         // Known to be broken in gcc 6.4 and 6.5 with optimizations
-         // Issue in gcc: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83116
-         EXPECT_TRUE(s1.size() == 4);
-         EXPECT_TRUE(s2.size() == 0);
- #else
-         EXPECT_TRUE(s1.size() == s2.size());
- #endif
-     }
- }
-
- TEST(span_ext_test, make_span_from_const_std_array_constructor)
- {
-     const std::array<int, 4> arr = {1, 2, 3, 4};
-
-     {
-         auto s = make_span(arr);
-         EXPECT_TRUE(s.size() == arr.size());
-         EXPECT_TRUE(s.data() == arr.data());
-     }
- }
-
- TEST(span_ext_test, make_span_from_std_array_const_constructor)
- {
-     std::array<const int, 4> arr = {1, 2, 3, 4};
-
-     {
-         auto s = make_span(arr);
-         EXPECT_TRUE(s.size() == arr.size());
-         EXPECT_TRUE(s.data() == arr.data());
-     }
- }
-
- TEST(span_ext_test, make_span_from_container_constructor)
- {
-     std::vector<int> v = {1, 2, 3};
-     const std::vector<int> cv = v;
-
-     {
-         auto s = make_span(v);
-         EXPECT_TRUE(s.size() == v.size());
-         EXPECT_TRUE(s.data() == v.data());
-
-         auto cs = make_span(cv);
-         EXPECT_TRUE(cs.size() == cv.size());
-         EXPECT_TRUE(cs.data() == cv.data());
-     }
- }
-
- TEST(span_test, interop_with_gsl_at)
- {
-     int arr[5] = {1, 2, 3, 4, 5};
-     span<int> s{arr};
-     EXPECT_TRUE(at(s, 0) ==  1);
-     EXPECT_TRUE(at(s, 1) == 2);
- }
-
- TEST(span_ext_test, iterator_free_functions)
- {
-     int a[] = {1, 2, 3, 4};
-     span<int> s{a};
-
-     EXPECT_TRUE((std::is_same<decltype(s.begin()), decltype(begin(s))>::value));
-     EXPECT_TRUE((std::is_same<decltype(s.end()), decltype(end(s))>::value));
-
-     EXPECT_TRUE((std::is_same<decltype(s.cbegin()), decltype(cbegin(s))>::value));
-     EXPECT_TRUE((std::is_same<decltype(s.cend()), decltype(cend(s))>::value));
-
-     EXPECT_TRUE((std::is_same<decltype(s.rbegin()), decltype(rbegin(s))>::value));
-     EXPECT_TRUE((std::is_same<decltype(s.rend()), decltype(rend(s))>::value));
-
-     EXPECT_TRUE((std::is_same<decltype(s.crbegin()), decltype(crbegin(s))>::value));
-     EXPECT_TRUE((std::is_same<decltype(s.crend()), decltype(crend(s))>::value));
-
-     EXPECT_TRUE(s.begin() == begin(s));
-     EXPECT_TRUE(s.end() == end(s));
-
-     EXPECT_TRUE(s.cbegin() == cbegin(s));
-     EXPECT_TRUE(s.cend() == cend(s));
-
-     EXPECT_TRUE(s.rbegin() == rbegin(s));
-     EXPECT_TRUE(s.rend() == rend(s));
-
-     EXPECT_TRUE(s.crbegin() == crbegin(s));
-     EXPECT_TRUE(s.crend() == crend(s));
- }
-
- TEST(span_ext_test, ssize_free_function)
- {
-     int a[] = {1, 2, 3, 4};
-     span<int> s{a};
-
-     EXPECT_FALSE((std::is_same<decltype(s.size()), decltype(ssize(s))>::value));
-     EXPECT_TRUE(s.size() == static_cast<std::size_t>(ssize(s)));
- }
-
-  TEST(span_ext_test, comparison_operators)
- {
-     {
-         span<int> s1;
-         span<int> s2;
-         EXPECT_TRUE(s1 == s2);
-         EXPECT_FALSE(s1 != s2);
-         EXPECT_FALSE(s1 < s2);
-         EXPECT_TRUE(s1 <= s2);
-         EXPECT_FALSE(s1 > s2);
-         EXPECT_TRUE(s1 >= s2);
-         EXPECT_TRUE(s2 == s1);
-         EXPECT_FALSE(s2 != s1);
-         EXPECT_FALSE(s2 != s1);
-         EXPECT_TRUE(s2 <= s1);
-         EXPECT_FALSE(s2 > s1);
-         EXPECT_TRUE(s2 >= s1);
-     }
-
-     {
-         int arr[] = {2, 1};
-         span<int> s1 = arr;
-         span<int> s2 = arr;
-
-         EXPECT_TRUE(s1 == s2);
-         EXPECT_FALSE(s1 != s2);
-         EXPECT_FALSE(s1 < s2);
-         EXPECT_TRUE(s1 <= s2);
-         EXPECT_FALSE(s1 > s2);
-         EXPECT_TRUE(s1 >= s2);
-         EXPECT_TRUE(s2 == s1);
-         EXPECT_FALSE(s2 != s1);
-         EXPECT_FALSE(s2 < s1);
-         EXPECT_TRUE(s2 <= s1);
-         EXPECT_FALSE(s2 > s1);
-         EXPECT_TRUE(s2 >= s1);
-     }
-
-     {
-         int arr[] = {2, 1}; // bigger
-
-         span<int> s1;
-         span<int> s2 = arr;
-
-         EXPECT_TRUE(s1 != s2);
-         EXPECT_TRUE(s2 != s1);
-         EXPECT_FALSE(s1 == s2);
-         EXPECT_FALSE(s2 == s1);
-         EXPECT_TRUE(s1 < s2);
-         EXPECT_FALSE(s2 < s1);
-         EXPECT_TRUE(s1 <= s2);
-         EXPECT_FALSE(s2 <= s1);
-         EXPECT_TRUE(s2 > s1);
-         EXPECT_FALSE(s1 > s2);
-         EXPECT_TRUE(s2 >= s1);
-         EXPECT_FALSE(s1 >= s2);
-     }
-
-     {
-         int arr1[] = {1, 2};
-         int arr2[] = {1, 2};
-         span<int> s1 = arr1;
-         span<int> s2 = arr2;
-
-         EXPECT_TRUE(s1 == s2);
-         EXPECT_FALSE(s1 != s2);
-         EXPECT_FALSE(s1 < s2);
-         EXPECT_TRUE(s1 <= s2);
-         EXPECT_FALSE(s1 > s2);
-         EXPECT_TRUE(s1 >= s2);
-         EXPECT_TRUE(s2 == s1);
-         EXPECT_FALSE(s2 != s1);
-         EXPECT_FALSE(s2 < s1);
-         EXPECT_TRUE(s2 <= s1);
-         EXPECT_FALSE(s2 > s1);
-         EXPECT_TRUE(s2 >= s1);
-     }
-
-     {
-         int arr[] = {1, 2, 3};
-
-         span<int> s1 = {&arr[0], 2}; // shorter
-         span<int> s2 = arr;          // longer
-
-         EXPECT_TRUE(s1 != s2);
-         EXPECT_TRUE(s2 != s1);
-         EXPECT_FALSE(s1 == s2);
-         EXPECT_FALSE(s2 == s1);
-         EXPECT_TRUE(s1 < s2);
-         EXPECT_FALSE(s2 < s1);
-         EXPECT_TRUE(s1 <= s2);
-         EXPECT_FALSE(s2 <= s1);
-         EXPECT_TRUE(s2 > s1);
-         EXPECT_FALSE(s1 > s2);
-         EXPECT_TRUE(s2 >= s1);
-         EXPECT_FALSE(s1 >= s2);
-     }
-
-     {
-         int arr1[] = {1, 2}; // smaller
-         int arr2[] = {2, 1}; // bigger
-
-         span<int> s1 = arr1;
-         span<int> s2 = arr2;
-
-         EXPECT_TRUE(s1 != s2);
-         EXPECT_TRUE(s2 != s1);
-         EXPECT_FALSE(s1 == s2);
-         EXPECT_FALSE(s2 == s1);
-         EXPECT_TRUE(s1 < s2);
-         EXPECT_FALSE(s2 < s1);
-         EXPECT_TRUE(s1 <= s2);
-         EXPECT_FALSE(s2 <= s1);
-         EXPECT_TRUE(s2 > s1);
-         EXPECT_FALSE(s1 > s2);
-         EXPECT_TRUE(s2 >= s1);
-         EXPECT_FALSE(s1 >= s2);
-     }
- }
+///////////////////////////////////////////////////////////////////////////////
+//
+// 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 <gtest/gtest.h>
+
+#include <gsl/gsl_util> // for narrow_cast, at
+#include <gsl/span_ext> // for operator==, operator!=, make_span
+
+#include <array>       // for array
+#include <iostream>    // for cerr
+#include <vector>      // for vector
+
+using namespace std;
+using namespace gsl;
+
+namespace
+{
+static constexpr char deathstring[] = "Expected Death";
+} // namespace
+
+TEST(span_ext_test, make_span_from_pointer_length_constructor)
+{
+    std::set_terminate([] {
+        std::cerr << "Expected Death. from_pointer_length_constructor";
+        std::abort();
+    });
+    int arr[4] = {1, 2, 3, 4};
+
+    {
+        auto s = make_span(&arr[0], 2);
+        EXPECT_TRUE(s.size() == 2);
+        EXPECT_TRUE(s.data() == &arr[0]);
+        EXPECT_TRUE(s[0] == 1);
+        EXPECT_TRUE(s[1] == 2);
+    }
+
+    {
+        int* p = nullptr;
+        auto s = make_span(p, narrow_cast<span<int>::size_type>(0));
+        EXPECT_TRUE(s.size() == 0);
+        EXPECT_TRUE(s.data() == nullptr);
+    }
+
+    {
+        int* p = nullptr;
+        auto workaround_macro = [=]() { make_span(p, 2); };
+        EXPECT_DEATH(workaround_macro(), deathstring);
+    }
+}
+
+TEST(span_ext_test, make_span_from_pointer_pointer_construction)
+{
+    int arr[4] = {1, 2, 3, 4};
+
+    {
+        auto s = make_span(&arr[0], &arr[2]);
+        EXPECT_TRUE(s.size() == 2);
+        EXPECT_TRUE(s.data() == &arr[0]);
+        EXPECT_TRUE(s[0] == 1);
+        EXPECT_TRUE(s[1] == 2);
+    }
+
+    {
+        auto s = make_span(&arr[0], &arr[0]);
+        EXPECT_TRUE(s.size() == 0);
+        EXPECT_TRUE(s.data() == &arr[0]);
+    }
+
+    {
+        int* p = nullptr;
+        auto s = make_span(p, p);
+        EXPECT_TRUE(s.size() == 0);
+        EXPECT_TRUE(s.data() == nullptr);
+    }
+}
+
+TEST(span_ext_test, make_span_from_array_constructor)
+ {
+     int arr[5] = {1, 2, 3, 4, 5};
+     int arr2d[2][3] = {1, 2, 3, 4, 5, 6};
+     int arr3d[2][3][2] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12};
+
+     {
+         const auto s = make_span(arr);
+         EXPECT_TRUE(s.size() == 5);
+         EXPECT_TRUE(s.data() == std::addressof(arr[0]));
+     }
+
+     {
+         const auto s = make_span(std::addressof(arr2d[0]), 1);
+         EXPECT_TRUE(s.size() == 1);
+         EXPECT_TRUE(s.data() == std::addressof(arr2d[0]));
+     }
+
+     {
+         const auto s = make_span(std::addressof(arr3d[0]), 1);
+         EXPECT_TRUE(s.size() == 1);
+         EXPECT_TRUE(s.data() == std::addressof(arr3d[0]));
+     }
+ }
+
+ TEST(span_ext_test, make_span_from_dynamic_array_constructor)
+ {
+     double(*arr)[3][4] = new double[100][3][4];
+
+     {
+         auto s = make_span(&arr[0][0][0], 10);
+         EXPECT_TRUE(s.size() == 10);
+         EXPECT_TRUE(s.data() == &arr[0][0][0]);
+     }
+
+     delete[] arr;
+ }
+
+ TEST(span_ext_test, make_span_from_std_array_constructor)
+ {
+     std::array<int, 4> arr = {1, 2, 3, 4};
+
+     {
+         auto s = make_span(arr);
+         EXPECT_TRUE(s.size() == arr.size());
+         EXPECT_TRUE(s.data() == arr.data());
+     }
+
+     // This test checks for the bug found in gcc 6.1, 6.2, 6.3, 6.4, 6.5 7.1, 7.2, 7.3 - issue #590
+     {
+         span<int> s1 = make_span(arr);
+
+         static span<int> s2;
+         s2 = s1;
+
+ #if defined(__GNUC__) && __GNUC__ == 6 && (__GNUC_MINOR__ == 4 || __GNUC_MINOR__ == 5) &&          \
+     __GNUC_PATCHLEVEL__ == 0 && defined(__OPTIMIZE__)
+         // Known to be broken in gcc 6.4 and 6.5 with optimizations
+         // Issue in gcc: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=83116
+         EXPECT_TRUE(s1.size() == 4);
+         EXPECT_TRUE(s2.size() == 0);
+ #else
+         EXPECT_TRUE(s1.size() == s2.size());
+ #endif
+     }
+ }
+
+ TEST(span_ext_test, make_span_from_const_std_array_constructor)
+ {
+     const std::array<int, 4> arr = {1, 2, 3, 4};
+
+     {
+         auto s = make_span(arr);
+         EXPECT_TRUE(s.size() == arr.size());
+         EXPECT_TRUE(s.data() == arr.data());
+     }
+ }
+
+ TEST(span_ext_test, make_span_from_std_array_const_constructor)
+ {
+     std::array<const int, 4> arr = {1, 2, 3, 4};
+
+     {
+         auto s = make_span(arr);
+         EXPECT_TRUE(s.size() == arr.size());
+         EXPECT_TRUE(s.data() == arr.data());
+     }
+ }
+
+ TEST(span_ext_test, make_span_from_container_constructor)
+ {
+     std::vector<int> v = {1, 2, 3};
+     const std::vector<int> cv = v;
+
+     {
+         auto s = make_span(v);
+         EXPECT_TRUE(s.size() == v.size());
+         EXPECT_TRUE(s.data() == v.data());
+
+         auto cs = make_span(cv);
+         EXPECT_TRUE(cs.size() == cv.size());
+         EXPECT_TRUE(cs.data() == cv.data());
+     }
+ }
+
+ TEST(span_test, interop_with_gsl_at)
+ {
+     int arr[5] = {1, 2, 3, 4, 5};
+     span<int> s{arr};
+     EXPECT_TRUE(at(s, 0) ==  1);
+     EXPECT_TRUE(at(s, 1) == 2);
+ }
+
+ TEST(span_ext_test, iterator_free_functions)
+ {
+     int a[] = {1, 2, 3, 4};
+     span<int> s{a};
+
+     EXPECT_TRUE((std::is_same<decltype(s.begin()), decltype(begin(s))>::value));
+     EXPECT_TRUE((std::is_same<decltype(s.end()), decltype(end(s))>::value));
+
+     EXPECT_TRUE((std::is_same<decltype(std::cbegin(s)), decltype(cbegin(s))>::value));
+     EXPECT_TRUE((std::is_same<decltype(std::cend(s)), decltype(cend(s))>::value));
+
+     EXPECT_TRUE((std::is_same<decltype(s.rbegin()), decltype(rbegin(s))>::value));
+     EXPECT_TRUE((std::is_same<decltype(s.rend()), decltype(rend(s))>::value));
+
+     EXPECT_TRUE((std::is_same<decltype(std::crbegin(s)), decltype(crbegin(s))>::value));
+     EXPECT_TRUE((std::is_same<decltype(std::crend(s)), decltype(crend(s))>::value));
+
+     EXPECT_TRUE(s.begin() == begin(s));
+     EXPECT_TRUE(s.end() == end(s));
+
+     EXPECT_TRUE(s.rbegin() == rbegin(s));
+     EXPECT_TRUE(s.rend() == rend(s));
+
+     EXPECT_TRUE(s.begin() == cbegin(s));
+     EXPECT_TRUE(s.end() == cend(s));
+
+     EXPECT_TRUE(s.rbegin() == crbegin(s));
+     EXPECT_TRUE(s.rend() == crend(s));
+ }
+
+ TEST(span_ext_test, ssize_free_function)
+ {
+     int a[] = {1, 2, 3, 4};
+     span<int> s{a};
+
+     EXPECT_FALSE((std::is_same<decltype(s.size()), decltype(ssize(s))>::value));
+     EXPECT_TRUE(s.size() == static_cast<std::size_t>(ssize(s)));
+ }
+
+  TEST(span_ext_test, comparison_operators)
+ {
+     {
+         span<int> s1;
+         span<int> s2;
+         EXPECT_TRUE(s1 == s2);
+         EXPECT_FALSE(s1 != s2);
+         EXPECT_FALSE(s1 < s2);
+         EXPECT_TRUE(s1 <= s2);
+         EXPECT_FALSE(s1 > s2);
+         EXPECT_TRUE(s1 >= s2);
+         EXPECT_TRUE(s2 == s1);
+         EXPECT_FALSE(s2 != s1);
+         EXPECT_FALSE(s2 != s1);
+         EXPECT_TRUE(s2 <= s1);
+         EXPECT_FALSE(s2 > s1);
+         EXPECT_TRUE(s2 >= s1);
+     }
+
+     {
+         int arr[] = {2, 1};
+         span<int> s1 = arr;
+         span<int> s2 = arr;
+
+         EXPECT_TRUE(s1 == s2);
+         EXPECT_FALSE(s1 != s2);
+         EXPECT_FALSE(s1 < s2);
+         EXPECT_TRUE(s1 <= s2);
+         EXPECT_FALSE(s1 > s2);
+         EXPECT_TRUE(s1 >= s2);
+         EXPECT_TRUE(s2 == s1);
+         EXPECT_FALSE(s2 != s1);
+         EXPECT_FALSE(s2 < s1);
+         EXPECT_TRUE(s2 <= s1);
+         EXPECT_FALSE(s2 > s1);
+         EXPECT_TRUE(s2 >= s1);
+     }
+
+     {
+         int arr[] = {2, 1}; // bigger
+
+         span<int> s1;
+         span<int> s2 = arr;
+
+         EXPECT_TRUE(s1 != s2);
+         EXPECT_TRUE(s2 != s1);
+         EXPECT_FALSE(s1 == s2);
+         EXPECT_FALSE(s2 == s1);
+         EXPECT_TRUE(s1 < s2);
+         EXPECT_FALSE(s2 < s1);
+         EXPECT_TRUE(s1 <= s2);
+         EXPECT_FALSE(s2 <= s1);
+         EXPECT_TRUE(s2 > s1);
+         EXPECT_FALSE(s1 > s2);
+         EXPECT_TRUE(s2 >= s1);
+         EXPECT_FALSE(s1 >= s2);
+     }
+
+     {
+         int arr1[] = {1, 2};
+         int arr2[] = {1, 2};
+         span<int> s1 = arr1;
+         span<int> s2 = arr2;
+
+         EXPECT_TRUE(s1 == s2);
+         EXPECT_FALSE(s1 != s2);
+         EXPECT_FALSE(s1 < s2);
+         EXPECT_TRUE(s1 <= s2);
+         EXPECT_FALSE(s1 > s2);
+         EXPECT_TRUE(s1 >= s2);
+         EXPECT_TRUE(s2 == s1);
+         EXPECT_FALSE(s2 != s1);
+         EXPECT_FALSE(s2 < s1);
+         EXPECT_TRUE(s2 <= s1);
+         EXPECT_FALSE(s2 > s1);
+         EXPECT_TRUE(s2 >= s1);
+     }
+
+     {
+         int arr[] = {1, 2, 3};
+
+         span<int> s1 = {&arr[0], 2}; // shorter
+         span<int> s2 = arr;          // longer
+
+         EXPECT_TRUE(s1 != s2);
+         EXPECT_TRUE(s2 != s1);
+         EXPECT_FALSE(s1 == s2);
+         EXPECT_FALSE(s2 == s1);
+         EXPECT_TRUE(s1 < s2);
+         EXPECT_FALSE(s2 < s1);
+         EXPECT_TRUE(s1 <= s2);
+         EXPECT_FALSE(s2 <= s1);
+         EXPECT_TRUE(s2 > s1);
+         EXPECT_FALSE(s1 > s2);
+         EXPECT_TRUE(s2 >= s1);
+         EXPECT_FALSE(s1 >= s2);
+     }
+
+     {
+         int arr1[] = {1, 2}; // smaller
+         int arr2[] = {2, 1}; // bigger
+
+         span<int> s1 = arr1;
+         span<int> s2 = arr2;
+
+         EXPECT_TRUE(s1 != s2);
+         EXPECT_TRUE(s2 != s1);
+         EXPECT_FALSE(s1 == s2);
+         EXPECT_FALSE(s2 == s1);
+         EXPECT_TRUE(s1 < s2);
+         EXPECT_FALSE(s2 < s1);
+         EXPECT_TRUE(s1 <= s2);
+         EXPECT_FALSE(s2 <= s1);
+         EXPECT_TRUE(s2 > s1);
+         EXPECT_FALSE(s1 > s2);
+         EXPECT_TRUE(s2 >= s1);
+         EXPECT_FALSE(s1 >= s2);
+     }
+ }
diff --git a/tests/span_tests.cpp b/tests/span_tests.cpp
index 689fff9..c5d978e 100644
--- a/tests/span_tests.cpp
+++ b/tests/span_tests.cpp
@@ -864,34 +864,6 @@ TEST(span_test, from_array_constructor)
      EXPECT_TRUE(it1 == it2);
  }
 
- TEST(span_test, const_iterator_default_init)
- {
-     span<int>::const_iterator it1;
-     span<int>::const_iterator it2;
-     EXPECT_TRUE(it1 == it2);
- }
-
- TEST(span_test, iterator_conversions)
- {
-     span<int>::iterator badIt;
-     span<int>::const_iterator badConstIt;
-     EXPECT_TRUE(badIt == badConstIt);
-
-     int a[] = {1, 2, 3, 4};
-     span<int> s = a;
-
-     auto it = s.begin();
-     auto cit = s.cbegin();
-
-     EXPECT_TRUE(it == cit);
-     EXPECT_TRUE(cit == it);
-
-     span<int>::const_iterator cit2 = it;
-     EXPECT_TRUE(cit2 == cit);
-
-     span<int>::const_iterator cit3 = it + 4;
-     EXPECT_TRUE(cit3 == s.cend());
- }
  TEST(span_test, iterator_comparisons)
  {
      int a[] = {1, 2, 3, 4};
@@ -899,15 +871,8 @@ TEST(span_test, from_array_constructor)
          span<int> s = a;
          span<int>::iterator it = s.begin();
          auto it2 = it + 1;
-         span<int>::const_iterator cit = s.cbegin();
 
-         EXPECT_TRUE(it == cit);
-         EXPECT_TRUE(cit == it);
          EXPECT_TRUE(it == it);
-         EXPECT_TRUE(cit == cit);
-         EXPECT_TRUE(cit == s.begin());
-         EXPECT_TRUE(s.begin() == cit);
-         EXPECT_TRUE(s.cbegin() == cit);
          EXPECT_TRUE(it == s.begin());
          EXPECT_TRUE(s.begin() == it);
 
@@ -916,26 +881,16 @@ TEST(span_test, from_array_constructor)
          EXPECT_TRUE(it != s.end());
          EXPECT_TRUE(it2 != s.end());
          EXPECT_TRUE(s.end() != it);
-         EXPECT_TRUE(it2 != cit);
-         EXPECT_TRUE(cit != it2);
 
          EXPECT_TRUE(it < it2);
          EXPECT_TRUE(it <= it2);
          EXPECT_TRUE(it2 <= s.end());
          EXPECT_TRUE(it < s.end());
-         EXPECT_TRUE(it <= cit);
-         EXPECT_TRUE(cit <= it);
-         EXPECT_TRUE(cit < it2);
-         EXPECT_TRUE(cit <= it2);
-         EXPECT_TRUE(cit < s.end());
-         EXPECT_TRUE(cit <= s.end());
 
          EXPECT_TRUE(it2 > it);
          EXPECT_TRUE(it2 >= it);
          EXPECT_TRUE(s.end() > it2);
          EXPECT_TRUE(s.end() >= it2);
-         EXPECT_TRUE(it2 > cit);
-         EXPECT_TRUE(it2 >= cit);
      }
  }
 
@@ -1019,63 +974,6 @@ TEST(span_test, from_array_constructor)
      }
  }
 
- TEST(span_test, cbegin_cend)
- {
-    std::set_terminate([] {
-        std::cerr << "Expected Death. cbegin_cend";
-        std::abort();
-    });
-     {
-         int a[] = {1, 2, 3, 4};
-         span<int> s = a;
-
-         span<int>::const_iterator cit = s.cbegin();
-         span<int>::const_iterator cit2 = std::cbegin(s);
-         EXPECT_TRUE(cit == cit2);
-
-         cit = s.cend();
-         cit2 = std::cend(s);
-         EXPECT_TRUE(cit == cit2);
-     }
-
-     {
-         int a[] = {1, 2, 3, 4};
-         span<int> s = a;
-
-         auto it = s.cbegin();
-         auto first = it;
-         EXPECT_TRUE(it == first);
-         EXPECT_TRUE(*it == 1);
-
-         auto beyond = s.cend();
-         EXPECT_TRUE(it != beyond);
-         EXPECT_DEATH(*beyond, deathstring);
-
-         EXPECT_TRUE(beyond - first == 4);
-         EXPECT_TRUE(first - first == 0);
-         EXPECT_TRUE(beyond - beyond == 0);
-
-         ++it;
-         EXPECT_TRUE(it - first == 1);
-         EXPECT_TRUE(*it == 2);
-         EXPECT_TRUE(beyond - it == 3);
-
-         int last = 0;
-         it = first;
-         EXPECT_TRUE(it == first);
-         while (it != s.cend())
-         {
-             EXPECT_TRUE(*it == last + 1);
-
-             last = *it;
-             ++it;
-         }
-
-         EXPECT_TRUE(it == beyond);
-         EXPECT_TRUE(it - beyond == 0);
-     }
- }
-
  TEST(span_test, rbegin_rend)
  {
     std::set_terminate([] {
@@ -1125,55 +1023,6 @@ TEST(span_test, from_array_constructor)
      }
  }
 
- TEST(span_test, crbegin_crend)
- {
-    std::set_terminate([] {
-        std::cerr << "Expected Death. crbegin_crend";
-        std::abort();
-    });
-     {
-         int a[] = {1, 2, 3, 4};
-         span<int> s = a;
-
-         auto it = s.crbegin();
-         auto first = it;
-         EXPECT_TRUE(it == first);
-         EXPECT_TRUE(*it == 4);
-
-         auto beyond = s.crend();
-         EXPECT_TRUE(it != beyond);
-#if (__cplusplus > 201402L)
-        EXPECT_DEATH([[maybe_unused]] auto _ = *beyond, deathstring);
-#else
-        EXPECT_DEATH(auto _ = *beyond, deathstring);
-#endif
-
-         EXPECT_TRUE(beyond - first == 4);
-         EXPECT_TRUE(first - first == 0);
-         EXPECT_TRUE(beyond - beyond == 0);
-
-         std::cout << *first << std::endl;
-         ++it;
-         EXPECT_TRUE(it - s.crbegin() == 1);
-         EXPECT_TRUE(*it == 3);
-         EXPECT_TRUE(beyond - it == 3);
-
-         it = first;
-         EXPECT_TRUE(it == first);
-         int last = 5;
-         while (it != s.crend())
-         {
-             EXPECT_TRUE(*it == last - 1);
-             last = *it;
-
-             ++it;
-         }
-
-         EXPECT_TRUE(it == beyond);
-         EXPECT_TRUE(it - beyond == 0);
-     }
- }
-
  TEST(span_test, as_bytes)
  {
      std::set_terminate([] {