Merge pull request #215 from neilmacintosh/dev/neilmac/span-rework

Reworked span to match GSL design.

include/gsl_assert.h

@@ -55,9 +55,9 @@ struct fail_fast : public std::runtime_error
 }
 
 #define Expects(cond)  if (!(cond)) \
-    throw gsl::fail_fast("GSL: Precondition failure at " __FILE__ GSL_STRINGIFY(__LINE__));
+    throw gsl::fail_fast("GSL: Precondition failure at " __FILE__ ": " GSL_STRINGIFY(__LINE__));
 #define Ensures(cond)  if (!(cond)) \
-    throw gsl::fail_fast("GSL: Postcondition failure at " __FILE__ GSL_STRINGIFY(__LINE__));
+    throw gsl::fail_fast("GSL: Postcondition failure at " __FILE__ ": " GSL_STRINGIFY(__LINE__));
 
 
 #elif defined(GSL_TERMINATE_ON_CONTRACT_VIOLATION)

include/gsl_util.h

@@ -76,23 +76,23 @@ private:
 
 // finally() - convenience function to generate a final_act
 template <class F>
-final_act<F> finally(const F &f)
+inline final_act<F> finally(const F &f)
 noexcept { return final_act<F>(f); }
 
 template <class F>
-final_act<F> finally(F &&f) noexcept
+inline final_act<F> finally(F &&f) noexcept
 { return final_act<F>(std::forward<F>(f)); }
 
 // narrow_cast(): a searchable way to do narrowing casts of values
 template<class T, class U>
-constexpr T narrow_cast(U u) noexcept
+inline constexpr T narrow_cast(U u) noexcept
 { return static_cast<T>(u); }
 
 struct narrowing_error : public std::exception {};
 
 // narrow() : a checked version of narrow_cast() that throws if the cast changed the value
 template<class T, class U>
-T narrow(U u)
+inline T narrow(U u)
 { T t = narrow_cast<T>(u); if (static_cast<U>(t) != u) throw narrowing_error(); return t; }
 
 //

tests/CMakeLists.txt

@@ -45,6 +45,7 @@ function(add_gsl_test name)
 endfunction()
 
 add_gsl_test(span_tests)
+add_gsl_test(strided_span_tests)
 add_gsl_test(string_span_tests)
 add_gsl_test(at_tests)
 add_gsl_test(bounds_tests)

tests/strided_span_tests.cpp

@@ -0,0 +1,748 @@
+/////////////////////////////////////////////////////////////////////////////// 
+// 
+// Copyright (c) 2015 Microsoft Corporation. All rights reserved. 
+// 
+// This code is licensed under the MIT License (MIT). 
+// 
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR 
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, 
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE 
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER 
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, 
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN 
+// THE SOFTWARE. 
+// 
+///////////////////////////////////////////////////////////////////////////////
+
+#include <UnitTest++/UnitTest++.h> 
+#include <span.h>
+
+#include <string>
+#include <vector>
+#include <list>
+#include <iostream>
+#include <memory>
+#include <map>
+
+using namespace std;
+using namespace gsl;
+
+namespace 
+{
+	struct BaseClass {};
+	struct DerivedClass : BaseClass {};
+}
+
+SUITE(strided_span_tests)
+{
+	TEST (span_section_test)
+	{
+		int a[30][4][5];
+		
+		auto av = as_span(a);
+		auto sub = av.section({15, 0, 0}, gsl::index<3>{2, 2, 2});
+		auto subsub = sub.section({1, 0, 0}, gsl::index<3>{1, 1, 1});
+		(void)subsub;
+	}
+
+	TEST(span_section)
+	{
+		std::vector<int> data(5 * 10);
+		std::iota(begin(data), end(data), 0);
+        const span<int, 5, 10> av = as_span(span<int>{data}, dim<5>(), dim<10>());
+
+		strided_span<int, 2> av_section_1 = av.section({ 1, 2 }, { 3, 4 });
+		CHECK((av_section_1[{0, 0}] == 12));
+		CHECK((av_section_1[{0, 1}] == 13));
+		CHECK((av_section_1[{1, 0}] == 22));
+		CHECK((av_section_1[{2, 3}] == 35));
+
+		strided_span<int, 2> av_section_2 = av_section_1.section({ 1, 2 }, { 2,2 });
+		CHECK((av_section_2[{0, 0}] == 24));
+		CHECK((av_section_2[{0, 1}] == 25));
+		CHECK((av_section_2[{1, 0}] == 34));
+	}
+
+	TEST(strided_span_constructors)
+	{
+		// Check stride constructor
+		{
+			int arr[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
+			const int carr[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9 };
+
+			strided_span<int, 1> sav1{ arr, {{9}, {1}} }; // T -> T
+			CHECK(sav1.bounds().index_bounds() == index<1>{ 9 });
+			CHECK(sav1.bounds().stride() == 1);
+			CHECK(sav1[0] == 1 && sav1[8] == 9);
+
+
+			strided_span<const int, 1> sav2{ carr, {{ 4 }, { 2 }} }; // const T -> const T
+			CHECK(sav2.bounds().index_bounds() == index<1>{ 4 });
+			CHECK(sav2.bounds().strides() == index<1>{2});
+			CHECK(sav2[0] == 1 && sav2[3] == 7);
+
+			strided_span<int, 2> sav3{ arr, {{ 2, 2 },{ 6, 2 }} }; // T -> const T
+			CHECK((sav3.bounds().index_bounds() == index<2>{ 2, 2 }));
+			CHECK((sav3.bounds().strides() == index<2>{ 6, 2 }));
+			CHECK((sav3[{0, 0}] == 1 && sav3[{0, 1}] == 3 && sav3[{1, 0}] == 7));
+		}
+
+		// Check span constructor
+		{
+			int arr[] = { 1, 2 };
+
+			// From non-cv-qualified source
+			{
+				const span<int> src = arr;
+
+				strided_span<int, 1> sav{ src, {2, 1} };
+				CHECK(sav.bounds().index_bounds() == index<1>{ 2 });
+				CHECK(sav.bounds().strides() == index<1>{ 1 });
+				CHECK(sav[1] == 2);
+
+#if _MSC_VER > 1800
+				//strided_span<const int, 1> sav_c{ {src}, {2, 1} };
+				strided_span<const int, 1> sav_c{ span<const int>{src}, strided_bounds<1>{2, 1} };
+#else
+				strided_span<const int, 1> sav_c{ span<const int>{src}, strided_bounds<1>{2, 1} };
+#endif
+				CHECK(sav_c.bounds().index_bounds() == index<1>{ 2 });
+				CHECK(sav_c.bounds().strides() == index<1>{ 1 });
+				CHECK(sav_c[1] == 2);
+
+#if _MSC_VER > 1800
+				strided_span<volatile int, 1> sav_v{ src, {2, 1} };
+#else
+				strided_span<volatile int, 1> sav_v{ span<volatile int>{src}, strided_bounds<1>{2, 1} };
+#endif
+				CHECK(sav_v.bounds().index_bounds() == index<1>{ 2 });
+				CHECK(sav_v.bounds().strides() == index<1>{ 1 });
+				CHECK(sav_v[1] == 2);
+
+#if _MSC_VER > 1800
+				strided_span<const volatile int, 1> sav_cv{ src, {2, 1} };
+#else
+				strided_span<const volatile int, 1> sav_cv{ span<const volatile int>{src}, strided_bounds<1>{2, 1} };
+#endif
+				CHECK(sav_cv.bounds().index_bounds() == index<1>{ 2 });
+				CHECK(sav_cv.bounds().strides() == index<1>{ 1 });
+				CHECK(sav_cv[1] == 2);
+			}
+
+			// From const-qualified source
+			{
+				const span<const int> src{ arr };
+
+				strided_span<const int, 1> sav_c{ src, {2, 1} };
+				CHECK(sav_c.bounds().index_bounds() == index<1>{ 2 });
+				CHECK(sav_c.bounds().strides() == index<1>{ 1 });
+				CHECK(sav_c[1] == 2);
+
+#if _MSC_VER > 1800
+				strided_span<const volatile int, 1> sav_cv{ src, {2, 1} };
+#else
+				strided_span<const volatile int, 1> sav_cv{ span<const volatile int>{src}, strided_bounds<1>{2, 1} };
+#endif
+				
+				CHECK(sav_cv.bounds().index_bounds() == index<1>{ 2 });
+				CHECK(sav_cv.bounds().strides() == index<1>{ 1 });
+				CHECK(sav_cv[1] == 2);
+			}
+
+			// From volatile-qualified source
+			{
+				const span<volatile int> src{ arr };
+
+				strided_span<volatile int, 1> sav_v{ src, {2, 1} };
+				CHECK(sav_v.bounds().index_bounds() == index<1>{ 2 });
+				CHECK(sav_v.bounds().strides() == index<1>{ 1 });
+				CHECK(sav_v[1] == 2);
+
+#if _MSC_VER > 1800
+				strided_span<const volatile int, 1> sav_cv{ src, {2, 1} };
+#else
+				strided_span<const volatile int, 1> sav_cv{ span<const volatile int>{src}, strided_bounds<1>{2, 1} };
+#endif
+				CHECK(sav_cv.bounds().index_bounds() == index<1>{ 2 });
+				CHECK(sav_cv.bounds().strides() == index<1>{ 1 });
+				CHECK(sav_cv[1] == 2);
+			}
+
+			// From cv-qualified source
+			{
+				const span<const volatile int> src{ arr };
+
+				strided_span<const volatile int, 1> sav_cv{ src, {2, 1} };
+				CHECK(sav_cv.bounds().index_bounds() == index<1>{ 2 });
+				CHECK(sav_cv.bounds().strides() == index<1>{ 1 });
+				CHECK(sav_cv[1] == 2);
+			}
+		}
+
+		// Check const-casting constructor
+		{
+			int arr[2] = { 4, 5 };
+
+			const span<int, 2> av(arr, 2);
+			span<const int, 2> av2{ av };
+			CHECK(av2[1] == 5);
+
+			static_assert(std::is_convertible<const span<int, 2>, span<const int, 2>>::value, "ctor is not implicit!");
+		
+			const strided_span<int, 1> src{ arr, {2, 1} };
+			strided_span<const int, 1> sav{ src };
+			CHECK(sav.bounds().index_bounds() == index<1>{ 2 });
+			CHECK(sav.bounds().stride() == 1);
+			CHECK(sav[1] == 5);
+			
+			static_assert(std::is_convertible<const strided_span<int, 1>, strided_span<const int, 1>>::value, "ctor is not implicit!");
+		}
+
+		// Check copy constructor
+		{
+			int arr1[2] = { 3, 4 };
+			const strided_span<int, 1> src1{ arr1, {2, 1} };
+			strided_span<int, 1> sav1{ src1 };
+ 
+			CHECK(sav1.bounds().index_bounds() == index<1>{ 2 });
+			CHECK(sav1.bounds().stride() == 1);
+			CHECK(sav1[0] == 3);
+
+			int arr2[6] = { 1, 2, 3, 4, 5, 6 };
+			const strided_span<const int, 2> src2{ arr2, {{ 3, 2 }, { 2, 1 }} };
+			strided_span<const int, 2> sav2{ src2 };
+			CHECK((sav2.bounds().index_bounds() == index<2>{ 3, 2 }));
+			CHECK((sav2.bounds().strides() == index<2>{ 2, 1 }));
+			CHECK((sav2[{0, 0}] == 1 && sav2[{2, 0}] == 5));
+		}
+
+		// Check const-casting assignment operator
+		{
+			int arr1[2] = { 1, 2 };
+			int arr2[6] = { 3, 4, 5, 6, 7, 8 };
+
+			const strided_span<int, 1> src{ arr1, {{2}, {1}} };
+			strided_span<const int, 1> sav{ arr2, {{3}, {2}} };
+			strided_span<const int, 1>& sav_ref = (sav = src);
+			CHECK(sav.bounds().index_bounds() == index<1>{ 2 });
+			CHECK(sav.bounds().strides() == index<1>{ 1 });
+			CHECK(sav[0] == 1);
+			CHECK(&sav_ref == &sav);
+		}
+		
+		// Check copy assignment operator
+		{
+			int arr1[2] = { 3, 4 };
+			int arr1b[1] = { 0 };
+			const strided_span<int, 1> src1{ arr1, {2, 1} };
+			strided_span<int, 1> sav1{ arr1b, {1, 1} };
+			strided_span<int, 1>& sav1_ref = (sav1 = src1);
+			CHECK(sav1.bounds().index_bounds() == index<1>{ 2 });
+			CHECK(sav1.bounds().strides() == index<1>{ 1 });
+			CHECK(sav1[0] == 3);
+			CHECK(&sav1_ref == &sav1);
+
+			const int arr2[6] = { 1, 2, 3, 4, 5, 6 };
+			const int arr2b[1] = { 0 };
+			const strided_span<const int, 2> src2{ arr2, {{ 3, 2 },{ 2, 1 }} };
+			strided_span<const int, 2> sav2{ arr2b, {{ 1, 1 },{ 1, 1 }} };
+			strided_span<const int, 2>& sav2_ref = (sav2 = src2);
+			CHECK((sav2.bounds().index_bounds() == index<2>{ 3, 2 }));
+			CHECK((sav2.bounds().strides() == index<2>{ 2, 1 }));
+			CHECK((sav2[{0, 0}] == 1 && sav2[{2, 0}] == 5));
+			CHECK(&sav2_ref == &sav2);
+		}
+	}
+
+	TEST(strided_span_slice)
+	{
+		std::vector<int> data(5 * 10);
+		std::iota(begin(data), end(data), 0);
+        const span<int, 5, 10> src = as_span(span<int>{data}, dim<5>(), dim<10>());
+
+		const strided_span<int, 2> sav{ src, {{5, 10}, {10, 1}} };
+#ifdef CONFIRM_COMPILATION_ERRORS
+		const strided_span<const int, 2> csav{ {src},{ { 5, 10 },{ 10, 1 } } };
+#endif
+		const strided_span<const int, 2> csav{ span<const int, 5, 10>{ src }, { { 5, 10 },{ 10, 1 } } };
+
+		strided_span<int, 1> sav_sl = sav[2];
+		CHECK(sav_sl[0] == 20);
+		CHECK(sav_sl[9] == 29);
+
+		strided_span<const int, 1> csav_sl = sav[3];
+		CHECK(csav_sl[0] == 30);
+		CHECK(csav_sl[9] == 39);
+
+		CHECK(sav[4][0] == 40);
+		CHECK(sav[4][9] == 49);
+	}
+
+	TEST(strided_span_column_major)
+	{
+		// strided_span may be used to accomodate more peculiar
+		// use cases, such as column-major multidimensional array
+		// (aka. "FORTRAN" layout).
+
+		int cm_array[3 * 5] = {
+			1, 4, 7, 10, 13,
+			2, 5, 8, 11, 14,
+			3, 6, 9, 12, 15
+		};
+		strided_span<int, 2> cm_sav{ cm_array, {{ 5, 3 },{ 1, 5 }} };
+
+		// Accessing elements
+		CHECK((cm_sav[{0, 0}] == 1));
+		CHECK((cm_sav[{0, 1}] == 2));
+		CHECK((cm_sav[{1, 0}] == 4));
+		CHECK((cm_sav[{4, 2}] == 15));
+
+		// Slice
+		strided_span<int, 1> cm_sl = cm_sav[3];
+
+		CHECK(cm_sl[0] == 10);
+		CHECK(cm_sl[1] == 11);
+		CHECK(cm_sl[2] == 12);
+
+		// Section 
+		strided_span<int, 2> cm_sec = cm_sav.section( { 2, 1 }, { 3, 2 });
+
+		CHECK((cm_sec.bounds().index_bounds() == index<2>{3, 2}));
+		CHECK((cm_sec[{0, 0}] == 8));
+		CHECK((cm_sec[{0, 1}] == 9));
+		CHECK((cm_sec[{1, 0}] == 11));
+		CHECK((cm_sec[{2, 1}] == 15));
+	}
+
+	TEST(strided_span_bounds)
+	{
+		int arr[] = { 0, 1, 2, 3 };
+		span<int> av(arr);
+
+		{
+			// incorrect sections
+			
+			CHECK_THROW(av.section(0, 0)[0], fail_fast);
+			CHECK_THROW(av.section(1, 0)[0], fail_fast);
+			CHECK_THROW(av.section(1, 1)[1], fail_fast);
+			
+			CHECK_THROW(av.section(2, 5), fail_fast);
+			CHECK_THROW(av.section(5, 2), fail_fast);
+			CHECK_THROW(av.section(5, 0), fail_fast);
+			CHECK_THROW(av.section(0, 5), fail_fast);
+			CHECK_THROW(av.section(5, 5), fail_fast);
+		}
+
+		{
+			// zero stride
+			strided_span<int, 1> sav{ av,{ { 4 },{} } };
+			CHECK(sav[0] == 0);
+			CHECK(sav[3] == 0);
+			CHECK_THROW(sav[4], fail_fast);
+		}
+
+		{
+			// zero extent
+			strided_span<int, 1> sav{ av,{ {},{ 1 } } };
+			CHECK_THROW(sav[0], fail_fast);
+		}
+
+		{
+			// zero extent and stride
+			strided_span<int, 1> sav{ av,{ {},{} } };
+			CHECK_THROW(sav[0], fail_fast);
+		}
+
+		{
+			// strided array ctor with matching strided bounds 
+			strided_span<int, 1> sav{ arr,{ 4, 1 } };
+			CHECK(sav.bounds().index_bounds() == index<1>{ 4 });
+			CHECK(sav[3] == 3);
+			CHECK_THROW(sav[4], fail_fast);
+		}
+
+		{
+			// strided array ctor with smaller strided bounds 
+			strided_span<int, 1> sav{ arr,{ 2, 1 } };
+			CHECK(sav.bounds().index_bounds() == index<1>{ 2 });
+			CHECK(sav[1] == 1);
+			CHECK_THROW(sav[2], fail_fast);
+		}
+
+		{
+			// strided array ctor with fitting irregular bounds 
+			strided_span<int, 1> sav{ arr,{ 2, 3 } };
+			CHECK(sav.bounds().index_bounds() == index<1>{ 2 });
+			CHECK(sav[0] == 0);
+			CHECK(sav[1] == 3);
+			CHECK_THROW(sav[2], fail_fast);
+		}
+
+		{
+			// bounds cross data boundaries - from static arrays
+			CHECK_THROW((strided_span<int, 1> { arr, { 3, 2 } }), fail_fast);
+			CHECK_THROW((strided_span<int, 1> { arr, { 3, 3 } }), fail_fast);
+			CHECK_THROW((strided_span<int, 1> { arr, { 4, 5 } }), fail_fast);
+			CHECK_THROW((strided_span<int, 1> { arr, { 5, 1 } }), fail_fast);
+			CHECK_THROW((strided_span<int, 1> { arr, { 5, 5 } }), fail_fast);
+		}
+
+		{
+			// bounds cross data boundaries - from array view
+			CHECK_THROW((strided_span<int, 1> { av, { 3, 2 } }), fail_fast);
+			CHECK_THROW((strided_span<int, 1> { av, { 3, 3 } }), fail_fast);
+			CHECK_THROW((strided_span<int, 1> { av, { 4, 5 } }), fail_fast);
+			CHECK_THROW((strided_span<int, 1> { av, { 5, 1 } }), fail_fast);
+			CHECK_THROW((strided_span<int, 1> { av, { 5, 5 } }), fail_fast);
+		}
+
+		{
+			// bounds cross data boundaries - from dynamic arrays
+			CHECK_THROW((strided_span<int, 1> { av.data(), 4, { 3, 2 } }), fail_fast);
+			CHECK_THROW((strided_span<int, 1> { av.data(), 4, { 3, 3 } }), fail_fast);
+			CHECK_THROW((strided_span<int, 1> { av.data(), 4, { 4, 5 } }), fail_fast);
+			CHECK_THROW((strided_span<int, 1> { av.data(), 4, { 5, 1 } }), fail_fast);
+			CHECK_THROW((strided_span<int, 1> { av.data(), 4, { 5, 5 } }), fail_fast);
+			CHECK_THROW((strided_span<int, 1> { av.data(), 2, { 2, 2 } }), fail_fast);
+		}
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+		{
+			strided_span<int, 1> sav0{ av.data(), { 3, 2 } };
+			strided_span<int, 1> sav1{ arr, { 1 } };
+			strided_span<int, 1> sav2{ arr, { 1,1,1 } };
+			strided_span<int, 1> sav3{ av, { 1 } };
+			strided_span<int, 1> sav4{ av, { 1,1,1 } };
+			strided_span<int, 2> sav5{ av.as_span(dim<2>(), dim<2>()), { 1 } };
+			strided_span<int, 2> sav6{ av.as_span(dim<2>(), dim<2>()), { 1,1,1 } };
+			strided_span<int, 2> sav7{ av.as_span(dim<2>(), dim<2>()), { { 1,1 },{ 1,1 },{ 1,1 } } };
+
+			index<1> index{ 0, 1 };
+			strided_span<int, 1> sav8{ arr,{ 1,{ 1,1 } } };
+			strided_span<int, 1> sav9{ arr,{ { 1,1 },{ 1,1 } } };
+			strided_span<int, 1> sav10{ av,{ 1,{ 1,1 } } };
+			strided_span<int, 1> sav11{ av,{ { 1,1 },{ 1,1 } } };
+			strided_span<int, 2> sav12{ av.as_span(dim<2>(), dim<2>()),{ { 1 },{ 1 } } };
+			strided_span<int, 2> sav13{ av.as_span(dim<2>(), dim<2>()),{ { 1 },{ 1,1,1 } } };
+			strided_span<int, 2> sav14{ av.as_span(dim<2>(), dim<2>()),{ { 1,1,1 },{ 1 } } };
+		}
+#endif
+	}
+
+	TEST(strided_span_type_conversion)
+	{
+		int arr[] = { 0, 1, 2, 3 };
+		span<int> av(arr);
+
+		{
+			strided_span<int, 1> sav{ av.data(), av.size(), { av.size() / 2, 2 } };
+#ifdef CONFIRM_COMPILATION_ERRORS
+			strided_span<long, 1> lsav1 = sav.as_strided_span<long, 1>();
+#endif
+		}
+		{
+			strided_span<int, 1> sav{ av, { av.size() / 2, 2 } };
+#ifdef CONFIRM_COMPILATION_ERRORS
+			strided_span<long, 1> lsav1 = sav.as_strided_span<long, 1>();
+#endif
+		}
+
+		span<const byte, dynamic_range> bytes = as_bytes(av);
+
+		// retype strided array with regular strides - from raw data
+		{
+			strided_bounds<2> bounds{ { 2, bytes.size() / 4 }, { bytes.size() / 2, 1 } };
+			strided_span<const byte, 2> sav2{ bytes.data(), bytes.size(), bounds };
+			strided_span<const int, 2> sav3 = sav2.as_strided_span<const int>();
+			CHECK(sav3[0][0] == 0);
+			CHECK(sav3[1][0] == 2);
+			CHECK_THROW(sav3[1][1], fail_fast);
+			CHECK_THROW(sav3[0][1], fail_fast);
+		}
+
+		// retype strided array with regular strides - from span
+		{
+			strided_bounds<2> bounds{ { 2, bytes.size() / 4 }, { bytes.size() / 2, 1 } };
+			span<const byte, 2, dynamic_range> bytes2 = as_span(bytes, dim<2>(), dim<>(bytes.size() / 2));
+			strided_span<const byte, 2> sav2{ bytes2, bounds };
+			strided_span<int, 2> sav3 = sav2.as_strided_span<int>();
+			CHECK(sav3[0][0] == 0);
+			CHECK(sav3[1][0] == 2);
+			CHECK_THROW(sav3[1][1], fail_fast);
+			CHECK_THROW(sav3[0][1], fail_fast);
+		}
+
+		// retype strided array with not enough elements - last dimension of the array is too small
+		{
+			strided_bounds<2> bounds{ { 4,2 },{ 4, 1 } };
+			span<const byte, 2, dynamic_range> bytes2 = as_span(bytes, dim<2>(), dim<>(bytes.size() / 2));
+			strided_span<const byte, 2> sav2{ bytes2, bounds };
+			CHECK_THROW(sav2.as_strided_span<int>(), fail_fast);
+		}
+
+		// retype strided array with not enough elements - strides are too small
+		{
+			strided_bounds<2> bounds{ { 4,2 },{ 2, 1 } };
+			span<const byte, 2, dynamic_range> bytes2 = as_span(bytes, dim<2>(), dim<>(bytes.size() / 2));
+			strided_span<const byte, 2> sav2{ bytes2, bounds };
+			CHECK_THROW(sav2.as_strided_span<int>(), fail_fast);
+		}
+
+		// retype strided array with not enough elements - last dimension does not divide by the new typesize
+		{
+			strided_bounds<2> bounds{ { 2,6 },{ 4, 1 } };
+			span<const byte, 2, dynamic_range> bytes2 = as_span(bytes, dim<2>(), dim<>(bytes.size() / 2));
+			strided_span<const byte, 2> sav2{ bytes2, bounds };
+			CHECK_THROW(sav2.as_strided_span<int>(), fail_fast);
+		}
+
+		// retype strided array with not enough elements - strides does not divide by the new typesize
+		{
+			strided_bounds<2> bounds{ { 2, 1 },{ 6, 1 } };
+			span<const byte, 2, dynamic_range> bytes2 = as_span(bytes, dim<2>(), dim<>(bytes.size() / 2));
+			strided_span<const byte, 2> sav2{ bytes2, bounds };
+			CHECK_THROW(sav2.as_strided_span<int>(), fail_fast);
+		}
+
+		// retype strided array with irregular strides - from raw data
+		{
+			strided_bounds<1> bounds{ bytes.size() / 2, 2 };
+			strided_span<const byte, 1> sav2{ bytes.data(), bytes.size(), bounds };
+			CHECK_THROW(sav2.as_strided_span<int>(), fail_fast);
+		}
+
+		// retype strided array with irregular strides - from span
+		{
+			strided_bounds<1> bounds{ bytes.size() / 2, 2 };
+			strided_span<const byte, 1> sav2{ bytes, bounds };
+			CHECK_THROW(sav2.as_strided_span<int>(), fail_fast);
+		}
+	}
+
+	TEST(empty_strided_spans)
+	{
+		{
+			span<int, 0> empty_av(nullptr);
+			strided_span<int, 1> empty_sav{ empty_av, { 0, 1 } };
+
+			CHECK(empty_sav.bounds().index_bounds() == index<1>{ 0 });
+			CHECK_THROW(empty_sav[0], fail_fast);
+			CHECK_THROW(empty_sav.begin()[0], fail_fast);
+			CHECK_THROW(empty_sav.cbegin()[0], fail_fast);
+
+			for (auto& v : empty_sav)
+			{
+                (void)v;
+				CHECK(false);
+			}
+		}
+
+		{
+			strided_span<int, 1> empty_sav{ nullptr, 0, { 0, 1 } };
+
+			CHECK(empty_sav.bounds().index_bounds() == index<1>{ 0 });
+			CHECK_THROW(empty_sav[0], fail_fast);
+			CHECK_THROW(empty_sav.begin()[0], fail_fast);
+			CHECK_THROW(empty_sav.cbegin()[0], fail_fast);
+
+			for (auto& v : empty_sav)
+			{
+                (void)v;
+				CHECK(false);
+			}
+		}
+	}
+
+    void iterate_every_other_element(span<int, dynamic_range> av)
+    {
+        // pick every other element
+
+        auto length = av.size() / 2;
+#if _MSC_VER > 1800
+        auto bounds = strided_bounds<1>({length}, {2});
+#else
+        auto bounds = strided_bounds<1>(index<1>{ length }, index<1>{ 2 });
+#endif
+        strided_span<int, 1> strided(&av.data()[1], av.size() - 1, bounds);
+
+        CHECK(strided.size() == length);
+        CHECK(strided.bounds().index_bounds()[0] == length);
+        for (auto i = 0; i < strided.size(); ++i)
+        {
+            CHECK(strided[i] == av[2 * i + 1]);
+        }
+
+        int idx = 0;
+        for (auto num : strided)
+        {
+            CHECK(num == av[2 * idx + 1]);
+            idx++;
+        }
+    }
+
+    TEST(strided_span_section_iteration)
+    {
+        int arr[8] = {4,0,5,1,6,2,7,3};
+
+        // static bounds
+        {
+            span<int, 8> av(arr, 8);
+            iterate_every_other_element(av);
+        }
+
+        // dynamic bounds
+        {
+            span<int, dynamic_range> av(arr, 8);
+            iterate_every_other_element(av);
+        }
+    }
+
+    TEST(dynamic_strided_span_section_iteration)
+    {
+        auto arr = new int[8];
+        for (int i = 0; i < 4; ++i)
+        {
+            arr[2 * i] = 4 + i;
+            arr[2 * i + 1] = i;
+        }
+
+        auto av = as_span(arr, 8);
+        iterate_every_other_element(av);
+
+        delete[] arr;
+    }
+
+    void iterate_second_slice(span<int, dynamic_range, dynamic_range, dynamic_range> av)
+    {
+        int expected[6] = {2,3,10,11,18,19};
+        auto section = av.section({0,1,0}, {3,1,2});
+
+        for (auto i = 0; i < section.extent<0>(); ++i)
+        {
+            for (auto j = 0; j < section.extent<1>(); ++j)
+                for (auto k = 0; k < section.extent<2>(); ++k)
+                {
+                    auto idx = index<3>{i,j,k}; // avoid braces in the CHECK macro
+                    CHECK(section[idx] == expected[2 * i + 2 * j + k]);
+                }
+        }
+
+        for (auto i = 0; i < section.extent<0>(); ++i)
+        {
+            for (auto j = 0; j < section.extent<1>(); ++j)
+                for (auto k = 0; k < section.extent<2>(); ++k)
+                    CHECK(section[i][j][k] == expected[2 * i + 2 * j + k]);
+        }
+
+        int i = 0;
+        for (auto num : section)
+        {
+            CHECK(num == expected[i]);
+            i++;
+        }
+    }
+
+    TEST(strided_span_section_iteration_3d)
+    {
+        int arr[3][4][2];
+        for (auto i = 0; i < 3; ++i)
+        {
+            for (auto j = 0; j < 4; ++j)
+                for (auto k = 0; k < 2; ++k)
+                    arr[i][j][k] = 8 * i + 2 * j + k;
+        }
+
+        {
+            span<int, 3, 4, 2> av = arr;
+            iterate_second_slice(av);
+        }
+    }
+
+    TEST(dynamic_strided_span_section_iteration_3d)
+    {
+        auto height = 12, width = 2;
+        auto size = height * width;
+
+        auto arr = new int[size];
+        for (auto i = 0; i < size; ++i)
+        {
+            arr[i] = i;
+        }
+
+        {
+            auto av = as_span(as_span(arr, 24), dim<3>(), dim<4>(), dim<2>());
+            iterate_second_slice(av);
+        }
+
+        {
+            auto av = as_span(as_span(arr, 24), dim<>(3), dim<4>(), dim<2>());
+            iterate_second_slice(av);
+        }
+
+        {
+            auto av = as_span(as_span(arr, 24), dim<3>(), dim<>(4), dim<2>());
+            iterate_second_slice(av);
+        }
+
+        {
+            auto av = as_span(as_span(arr, 24), dim<3>(), dim<4>(), dim<>(2));
+            iterate_second_slice(av);
+        }
+        delete[] arr;
+    }
+
+    TEST(strided_span_conversion)
+    {
+        // get an span of 'c' values from the list of X's
+
+        struct X { int a; int b; int c; };
+
+        X arr[4] = {{0,1,2},{3,4,5},{6,7,8},{9,10,11}};
+
+        int s = sizeof(int) / sizeof(byte);
+        auto d2 = 3 * s;
+        auto d1 = sizeof(int) * 12 / d2;
+
+        // convert to 4x12 array of bytes
+        auto av = as_span(as_bytes(as_span(arr, 4)), dim<>(d1), dim<>(d2));
+
+        CHECK(av.bounds().index_bounds()[0] == 4);
+        CHECK(av.bounds().index_bounds()[1] == 12);
+
+        // get the last 4 columns
+        auto section = av.section({0, 2 * s}, {4, s}); // { { arr[0].c[0], arr[0].c[1], arr[0].c[2], arr[0].c[3] } , { arr[1].c[0], ... } , ... }
+
+                                                       // convert to array 4x1 array of integers
+        auto cs = section.as_strided_span<int>(); // { { arr[0].c }, {arr[1].c } , ... } 
+
+        CHECK(cs.bounds().index_bounds()[0] == 4);
+        CHECK(cs.bounds().index_bounds()[1] == 1);
+
+        // transpose to 1x4 array 
+        strided_bounds<2> reverse_bounds{
+            {cs.bounds().index_bounds()[1] , cs.bounds().index_bounds()[0]},
+            {cs.bounds().strides()[1], cs.bounds().strides()[0]}
+        };
+
+        strided_span<int, 2> transposed{cs.data(), cs.bounds().total_size(), reverse_bounds};
+
+        // slice to get a one-dimensional array of c's
+        strided_span<int, 1> result = transposed[0];
+
+        CHECK(result.bounds().index_bounds()[0] == 4);
+        CHECK_THROW(result.bounds().index_bounds()[1], fail_fast);
+
+        int i = 0;
+        for (auto& num : result)
+        {
+            CHECK(num == arr[i].c);
+            i++;
+        }
+
+    }
+}
+
+int main(int, const char *[])
+{
+	return UnitTest::RunAllTests();
+}

tests/string_span_tests.cpp

@@ -58,25 +58,21 @@ SUITE(string_span_tests)
         {
             cwstring_span<> v = ensure_z(stack_string);
             CHECK(v.length() == 5);
-            CHECK(v.used_length() == v.length());
         }
 
         {
             cwstring_span<> v = stack_string;
             CHECK(v.length() == 6);
-            CHECK(v.used_length() == v.length());
         }
 
         {
             wstring_span<> v = ensure_z(stack_string);
             CHECK(v.length() == 5);
-            CHECK(v.used_length() == v.length());
         }
 
         {
             wstring_span<> v = stack_string;
             CHECK(v.length() == 6);
-            CHECK(v.used_length() == v.length());
         }
 	}
 
@@ -85,7 +81,6 @@ SUITE(string_span_tests)
         const char* s = "Hello";
         cstring_span<> v = ensure_z(s);
         CHECK(v.length() == 5);
-        CHECK(v.used_length() == v.length());
     }
 
     TEST(TestConversionToConst)