Added new span-related files.

1 files changed, 1680 insertions, 0 deletions

diff --git a/tests/span_tests.cpp b/tests/span_tests.cpp
new file mode 100644
index 0000000..83eec0e
--- /dev/null
+++ b/tests/span_tests.cpp
@@ -0,0 +1,1680 @@
+///////////////////////////////////////////////////////////////////////////////
+//
+// 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 <iostream>
+#include <list>
+#include <map>
+#include <memory>
+#include <string>
+#include <vector>
+
+using namespace std;
+using namespace gsl;
+
+namespace
+{
+struct BaseClass
+{
+};
+struct DerivedClass : BaseClass
+{
+};
+}
+
+SUITE(span_tests)
+{
+#if 0
+    TEST(default_constructor)
+    {
+        {
+            span<int> s;
+            CHECK(s.length() == 0 && s.data() == nullptr);
+
+            span<const int> cs;
+            CHECK(cs.length() == 0 && cs.data() == nullptr);
+        }
+
+        {
+            span<int, 0> s;
+            CHECK(s.length() == 0 && s.data() == nullptr);
+
+            span<const int, 0> cs;
+            CHECK(cs.length() == 0 && cs.data() == nullptr);
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            span<int, 1> s;
+            CHECK(s.length() == 1 && s.data() == nullptr); // explains why it can't compile
+#endif
+        }
+
+        {
+            span<int> s{};
+            CHECK(s.length() == 0 && s.data() == nullptr);
+
+            span<const int> cs{};
+            CHECK(cs.length() == 0 && cs.data() == nullptr);
+        }
+    }
+
+    TEST(from_nullptr_constructor)
+    {
+        {
+            span<int> s = nullptr;
+            CHECK(s.length() == 0 && s.data() == nullptr);
+
+            span<const int> cs = nullptr;
+            CHECK(cs.length() == 0 && cs.data() == nullptr);
+        }
+
+        {
+            span<int, 0> s = nullptr;
+            CHECK(s.length() == 0 && s.data() == nullptr);
+
+            span<const int, 0> cs = nullptr;
+            CHECK(cs.length() == 0 && cs.data() == nullptr);
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            span<int, 1> s = nullptr;
+            CHECK(s.length() == 1 && s.data() == nullptr); // explains why it can't compile
+#endif
+        }
+
+        {
+            span<int> s{nullptr};
+            CHECK(s.length() == 0 && s.data() == nullptr);
+
+            span<const int> cs{nullptr};
+            CHECK(cs.length() == 0 && cs.data() == nullptr);
+        }
+
+        {
+            span<int*> s{nullptr};
+            CHECK(s.length() == 0 && s.data() == nullptr);
+
+            span<const int*> cs{nullptr};
+            CHECK(cs.length() == 0 && cs.data() == nullptr);
+        }
+    }
+
+    TEST(from_nullptr_length_constructor)
+    {
+        {
+            span<int> s{nullptr, 0};
+            CHECK(s.length() == 0 && s.data() == nullptr);
+
+            span<const int> cs{nullptr, 0};
+            CHECK(cs.length() == 0 && cs.data() == nullptr);
+        }
+
+        {
+            span<int, 0> s{nullptr, 0};
+            CHECK(s.length() == 0 && s.data() == nullptr);
+
+            span<const int, 0> cs{nullptr, 0};
+            CHECK(cs.length() == 0 && cs.data() == nullptr);
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            span<int, 1> s{nullptr, 0};
+            CHECK(s.length() == 1 && s.data() == nullptr); // explains why it can't compile
+#endif
+        }
+
+        {
+            auto workaround_macro = []() { span<int> s{nullptr, 1}; };
+            CHECK_THROW(workaround_macro(), fail_fast);
+
+            auto const_workaround_macro = []() { span<const int> cs{nullptr, 1}; };
+            CHECK_THROW(const_workaround_macro(), fail_fast);
+        }
+
+        {
+            auto workaround_macro = []() { span<int, 0> s{nullptr, 1}; };
+            CHECK_THROW(workaround_macro(), fail_fast);
+
+            auto const_workaround_macro = []() { span<const int, 0> s{nullptr, 1}; };
+            CHECK_THROW(const_workaround_macro(), fail_fast);
+        }
+
+        {
+            span<int*> s{nullptr, 0};
+            CHECK(s.length() == 0 && s.data() == nullptr);
+
+            span<const int*> cs{nullptr, 0};
+            CHECK(cs.length() == 0 && cs.data() == nullptr);
+        }
+    }
+
+    TEST(from_element_constructor)
+    {
+        int i = 5;
+
+        {
+            span<int> s = i;
+            CHECK(s.length() == 1 && s.data() == &i);
+            CHECK(s[0] == 5);
+
+            span<const int> cs = i;
+            CHECK(cs.length() == 1 && cs.data() == &i);
+            CHECK(cs[0] == 5);
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            const j = 1;
+            span<int, 0> s = j;
+#endif
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            span<int, 0> s = i;
+            CHECK(s.length() == 0 && s.data() == &i);
+#endif
+        }
+
+        {
+            span<int, 1> s = i;
+            CHECK(s.length() == 1 && s.data() == &i);
+            CHECK(s[0] == 5);
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            span<int, 2> s = i;
+            CHECK(s.length() == 2 && s.data() == &i);
+#endif
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            auto get_a_temp = []() -> int { return 4; };
+            auto use_a_span = [](span<int> s) { (void) s; };
+            use_a_span(get_a_temp());
+#endif
+        }
+    }
+
+    TEST(from_pointer_length_constructor)
+    {
+        int arr[4] = {1, 2, 3, 4};
+
+        {
+            span<int> s{&arr[0], 2};
+            CHECK(s.length() == 2 && s.data() == &arr[0]);
+            CHECK(s[0] == 1 && s[1] == 2);
+        }
+
+        {
+            span<int, 2> s{&arr[0], 2};
+            CHECK(s.length() == 2 && s.data() == &arr[0]);
+            CHECK(s[0] == 1 && s[1] == 2);
+        }
+
+        {
+            int* p = nullptr;
+            span<int> s{p, 0};
+            CHECK(s.length() == 0 && s.data() == nullptr);
+        }
+
+        {
+            int* p = nullptr;
+            auto workaround_macro = [=]() { span<int> s{p, 2}; };
+            CHECK_THROW(workaround_macro(), fail_fast);
+        }
+    }
+
+    TEST(from_pointer_pointer_constructor)
+    {
+        int arr[4] = {1, 2, 3, 4};
+
+        {
+            span<int> s{&arr[0], &arr[2]};
+            CHECK(s.length() == 2 && s.data() == &arr[0]);
+            CHECK(s[0] == 1 && s[1] == 2);
+        }
+
+        {
+            span<int, 2> s{&arr[0], &arr[2]};
+            CHECK(s.length() == 2 && s.data() == &arr[0]);
+            CHECK(s[0] == 1 && s[1] == 2);
+        }
+
+        {
+            span<int> s{&arr[0], &arr[0]};
+            CHECK(s.length() == 0 && s.data() == &arr[0]);
+        }
+
+        {
+            span<int, 0> s{&arr[0], &arr[0]};
+            CHECK(s.length() == 0 && s.data() == &arr[0]);
+        }
+
+        {
+            auto workaround_macro = [&]() { span<int> s{&arr[1], &arr[0]}; };
+            CHECK_THROW(workaround_macro(), fail_fast);
+        }
+
+        {
+            int* p = nullptr;
+            auto workaround_macro = [&]() { span<int> s{&arr[0], p}; };
+            CHECK_THROW(workaround_macro(), fail_fast);
+        }
+
+        {
+            int* p = nullptr;
+            auto workaround_macro = [&]() { span<int> s{p, p}; };
+            CHECK_THROW(workaround_macro(), fail_fast);
+        }
+
+        {
+            int* p = nullptr;
+            auto workaround_macro = [&]() { span<int> s{&arr[0], p}; };
+            CHECK_THROW(workaround_macro(), fail_fast);
+        }
+    }
+
+    TEST(from_array_constructor)
+    {
+        int arr[5] = {1, 2, 3, 4, 5};
+
+        {
+            span<int> s{arr};
+            CHECK(s.length() == 5 && s.data() == &arr[0]);
+        }
+
+        {
+            span<int, 5> s{arr};
+            CHECK(s.length() == 5 && s.data() == &arr[0]);
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            span<int, 6> s{arr};
+#endif
+        }
+
+        {
+            span<int, 0> s{arr};
+            CHECK(s.length() == 0 && s.data() == &arr[0]);
+        }
+
+        int arr2d[2][3] = {1, 2, 3, 4, 5, 6};
+
+        {
+            span<int> s{arr2d};
+            CHECK(s.length() == 6 && s.data() == &arr2d[0][0]);
+            CHECK(s[0] == 1 && s[5] == 6);
+        }
+
+        {
+            span<int, 0> s{arr2d};
+            CHECK(s.length() == 0 && s.data() == &arr2d[0][0]);
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            span<int, 5> s{arr2d};
+#endif
+        }
+
+        {
+            span<int, 6> s{arr2d};
+            CHECK(s.length() == 6 && s.data() == &arr2d[0][0]);
+            CHECK(s[0] == 1 && s[5] == 6);
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            span<int, 7> s{arr2d};
+#endif
+        }
+
+        {
+            span<int[3]> s{arr2d[0]};
+            CHECK(s.length() == 1 && s.data() == &arr2d[0]);
+        }
+
+        {
+            span<int, 2, 3> s{arr2d};
+            CHECK(s.length() == 6 && s.data() == &arr2d[0][0]);
+            auto workaround_macro = [&]() { return s[{1, 2}] == 6; };
+            CHECK(workaround_macro());
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            span<int, 3, 3> s{arr2d};
+#endif
+        }
+
+        int arr3d[2][3][2] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12};
+
+        {
+            span<int> s{arr3d};
+            CHECK(s.length() == 12 && s.data() == &arr3d[0][0][0]);
+            CHECK(s[0] == 1 && s[11] == 12);
+        }
+
+        {
+            span<int, 0> s{arr3d};
+            CHECK(s.length() == 0 && s.data() == &arr3d[0][0][0]);
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            span<int, 11> s{arr3d};
+#endif
+        }
+
+        {
+            span<int, 12> s{arr3d};
+            CHECK(s.length() == 12 && s.data() == &arr3d[0][0][0]);
+            CHECK(s[0] == 1 && s[5] == 6);
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            span<int, 13> s{arr3d};
+#endif
+        }
+
+        {
+            span<int[3][2]> s{arr3d[0]};
+            CHECK(s.length() == 1 && s.data() == &arr3d[0]);
+        }
+
+        {
+            span<int, 3, 2, 2> s{arr3d};
+            CHECK(s.length() == 12 && s.data() == &arr3d[0][0][0]);
+            auto workaround_macro = [&]() { return s[{2, 1, 0}] == 11; };
+            CHECK(workaround_macro());
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            span<int, 3, 3, 3> s{arr3d};
+#endif
+        }
+    }
+
+    TEST(from_dynamic_array_constructor)
+    {
+        double(*arr)[3][4] = new double[100][3][4];
+
+        {
+            span<double, dynamic_range, 3, 4> s(arr, 10);
+            CHECK(s.length() == 120 && s.data() == &arr[0][0][0]);
+            CHECK_THROW(s[10][3][4], fail_fast);
+        }
+
+        {
+            span<double, dynamic_range, 4, 3> s(arr, 10);
+            CHECK(s.length() == 120 && s.data() == &arr[0][0][0]);
+        }
+
+        {
+            span<double> s(arr, 10);
+            CHECK(s.length() == 120 && s.data() == &arr[0][0][0]);
+        }
+
+        {
+            span<double, dynamic_range, 3, 4> s(arr, 0);
+            CHECK(s.length() == 0 && s.data() == &arr[0][0][0]);
+        }
+
+        delete[] arr;
+    }
+
+    TEST(from_std_array_constructor)
+    {
+        std::array<int, 4> arr = {1, 2, 3, 4};
+
+        {
+            span<int> s{arr};
+            CHECK(s.size() == narrow_cast<ptrdiff_t>(arr.size()) && s.data() == arr.data());
+
+            span<const int> cs{arr};
+            CHECK(cs.size() == narrow_cast<ptrdiff_t>(arr.size()) && cs.data() == arr.data());
+        }
+
+        {
+            span<int, 4> s{arr};
+            CHECK(s.size() == narrow_cast<ptrdiff_t>(arr.size()) && s.data() == arr.data());
+
+            span<const int, 4> cs{arr};
+            CHECK(cs.size() == narrow_cast<ptrdiff_t>(arr.size()) && cs.data() == arr.data());
+        }
+
+        {
+            span<int, 2> s{arr};
+            CHECK(s.size() == 2 && s.data() == arr.data());
+
+            span<const int, 2> cs{arr};
+            CHECK(cs.size() == 2 && cs.data() == arr.data());
+        }
+
+        {
+            span<int, 0> s{arr};
+            CHECK(s.size() == 0 && s.data() == arr.data());
+
+            span<const int, 0> cs{arr};
+            CHECK(cs.size() == 0 && cs.data() == arr.data());
+        }
+
+        // TODO This is currently an unsupported scenario. We will come back to it as we revise
+        // the multidimensional interface and what transformations between dimensionality look like
+        //{
+        //    span<int, 2, 2> s{arr};
+        //    CHECK(s.size() == narrow_cast<ptrdiff_t>(arr.size()) && s.data() == arr.data());
+        //}
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            span<int, 5> s{arr};
+#endif
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            auto get_an_array = []() { return std::array<int, 4>{1, 2, 3, 4}; };
+            auto take_a_span = [](span<int> s) { (void) s; };
+            // try to take a temporary std::array
+            take_a_span(get_an_array());
+#endif
+        }
+    }
+
+    TEST(from_const_std_array_constructor)
+    {
+        const std::array<int, 4> arr = {1, 2, 3, 4};
+
+        {
+            span<const int> s{arr};
+            CHECK(s.size() == narrow_cast<ptrdiff_t>(arr.size()) && s.data() == arr.data());
+        }
+
+        {
+            span<const int, 4> s{arr};
+            CHECK(s.size() == narrow_cast<ptrdiff_t>(arr.size()) && s.data() == arr.data());
+        }
+
+        {
+            span<const int, 2> s{arr};
+            CHECK(s.size() == 2 && s.data() == arr.data());
+        }
+
+        {
+            span<const int, 0> s{arr};
+            CHECK(s.size() == 0 && s.data() == arr.data());
+        }
+
+        // TODO This is currently an unsupported scenario. We will come back to it as we revise
+        // the multidimensional interface and what transformations between dimensionality look like
+        //{
+        //    span<int, 2, 2> s{arr};
+        //    CHECK(s.size() == narrow_cast<ptrdiff_t>(arr.size()) && s.data() == arr.data());
+        //}
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            span<const int, 5> s{arr};
+#endif
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            auto get_an_array = []() -> const std::array<int, 4> { return {1, 2, 3, 4}; };
+            auto take_a_span = [](span<const int> s) { (void) s; };
+            // try to take a temporary std::array
+            take_a_span(get_an_array());
+#endif
+        }
+    }
+
+    TEST(from_container_constructor)
+    {
+        std::vector<int> v = {1, 2, 3};
+        const std::vector<int> cv = v;
+
+        {
+            span<int> s{v};
+            CHECK(s.size() == narrow_cast<std::ptrdiff_t>(v.size()) && s.data() == v.data());
+
+            span<const int> cs{v};
+            CHECK(cs.size() == narrow_cast<std::ptrdiff_t>(v.size()) && cs.data() == v.data());
+        }
+
+        std::string str = "hello";
+        const std::string cstr = "hello";
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            span<char> s{str};
+            CHECK(s.size() == narrow_cast<std::ptrdiff_t>(str.size()) && s.data() == str.data());
+#endif
+            span<const char> cs{str};
+            CHECK(cs.size() == narrow_cast<std::ptrdiff_t>(str.size()) && cs.data() == str.data());
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            span<char> s{cstr};
+#endif
+            span<const char> cs{cstr};
+            CHECK(cs.size() == narrow_cast<std::ptrdiff_t>(cstr.size()) &&
+                  cs.data() == cstr.data());
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            auto get_temp_vector = []() -> std::vector<int> { return {}; };
+            auto use_span = [](span<int> s) { (void) s; };
+            use_span(get_temp_vector());
+#endif
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            auto get_temp_string = []() -> std::string { return {}; };
+            auto use_span = [](span<char> s) { (void) s; };
+            use_span(get_temp_string());
+#endif
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            auto get_temp_vector = []() -> const std::vector<int> { return {}; };
+            auto use_span = [](span<const char> s) { (void) s; };
+            use_span(get_temp_vector());
+#endif
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            auto get_temp_string = []() -> const std::string { return {}; };
+            auto use_span = [](span<const char> s) { (void) s; };
+            use_span(get_temp_string());
+#endif
+        }
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            std::map<int, int> m;
+            span<int> s{m};
+#endif
+        }
+    }
+
+    TEST(from_convertible_span_constructor)
+    {
+#ifdef CONFIRM_COMPILATION_ERRORS
+        span<int, 7, 4, 2> av1(nullptr, b1);
+
+        auto f = [&]() { span<int, 7, 4, 2> av1(nullptr); };
+        CHECK_THROW(f(), fail_fast);
+#endif
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+        static_bounds<size_t, 7, dynamic_range, 2> b12(b11);
+        b12 = b11;
+        b11 = b12;
+
+        span<int, dynamic_range> av1 = nullptr;
+        span<int, 7, dynamic_range, 2> av2(av1);
+        span<int, 7, 4, 2> av2(av1);
+#endif
+
+        span<DerivedClass> avd;
+#ifdef CONFIRM_COMPILATION_ERRORS
+        span<BaseClass> avb = avd;
+#endif
+        span<const DerivedClass> avcd = avd;
+        (void) avcd;
+    }
+
+    TEST(copy_move_and_assignment)
+    {
+        span<int> s1;
+        CHECK(s1.empty());
+
+        int arr[] = {3, 4, 5};
+
+        span<const int> s2 = arr;
+        CHECK(s2.length() == 3 && s2.data() == &arr[0]);
+
+        s2 = s1;
+        CHECK(s2.empty());
+
+        auto get_temp_span = [&]() -> span<int> { return {&arr[1], 2}; };
+        auto use_span = [&](span<const int> s) { CHECK(s.length() == 2 && s.data() == &arr[1]); };
+        use_span(get_temp_span());
+
+        s1 = get_temp_span();
+        CHECK(s1.length() == 2 && s1.data() == &arr[1]);
+    }
+
+    template <class Bounds>
+    void fn(const Bounds&)
+    {
+        static_assert(Bounds::static_size == 60, "static bounds is wrong size");
+    }
+    TEST(as_span_reshape)
+    {
+        int a[3][4][5];
+        auto av = as_span(a);
+        fn(av.bounds());
+        auto av2 = as_span(av, dim<60>());
+        auto av3 = as_span(av2, dim<3>(), dim<4>(), dim<5>());
+        auto av4 = as_span(av3, dim<4>(), dim<>(3), dim<5>());
+        auto av5 = as_span(av4, dim<3>(), dim<4>(), dim<5>());
+        auto av6 = as_span(av5, dim<12>(), dim<>(5));
+
+        fill(av6.begin(), av6.end(), 1);
+
+        auto av7 = as_bytes(av6);
+
+        auto av8 = as_span<int>(av7);
+
+        CHECK(av8.size() == av6.size());
+        for (auto i = 0; i < av8.size(); i++) {
+            CHECK(av8[i] == 1);
+        }
+    }
+
+    TEST(first)
+    {
+        int arr[5] = {1, 2, 3, 4, 5};
+
+        {
+            span<int, 5> av = arr;
+            CHECK((av.first<2>().bounds() == static_bounds<2>()));
+            CHECK(av.first<2>().length() == 2);
+            CHECK(av.first(2).length() == 2);
+        }
+
+        {
+            span<int, 5> av = arr;
+            CHECK((av.first<0>().bounds() == static_bounds<0>()));
+            CHECK(av.first<0>().length() == 0);
+            CHECK(av.first(0).length() == 0);
+        }
+
+        {
+            span<int, 5> av = arr;
+            CHECK((av.first<5>().bounds() == static_bounds<5>()));
+            CHECK(av.first<5>().length() == 5);
+            CHECK(av.first(5).length() == 5);
+        }
+
+        {
+            span<int, 5> av = arr;
+#ifdef CONFIRM_COMPILATION_ERRORS
+            CHECK(av.first<6>().bounds() == static_bounds<6>());
+            CHECK(av.first<6>().length() == 6);
+            CHECK(av.first<-1>().length() == -1);
+#endif
+            CHECK_THROW(av.first(6).length(), fail_fast);
+        }
+
+        {
+            span<int, dynamic_range> av;
+            CHECK((av.first<0>().bounds() == static_bounds<0>()));
+            CHECK(av.first<0>().length() == 0);
+            CHECK(av.first(0).length() == 0);
+        }
+    }
+
+    TEST(last)
+    {
+        int arr[5] = {1, 2, 3, 4, 5};
+
+        {
+            span<int, 5> av = arr;
+            CHECK((av.last<2>().bounds() == static_bounds<2>()));
+            CHECK(av.last<2>().length() == 2);
+            CHECK(av.last(2).length() == 2);
+        }
+
+        {
+            span<int, 5> av = arr;
+            CHECK((av.last<0>().bounds() == static_bounds<0>()));
+            CHECK(av.last<0>().length() == 0);
+            CHECK(av.last(0).length() == 0);
+        }
+
+        {
+            span<int, 5> av = arr;
+            CHECK((av.last<5>().bounds() == static_bounds<5>()));
+            CHECK(av.last<5>().length() == 5);
+            CHECK(av.last(5).length() == 5);
+        }
+
+        {
+            span<int, 5> av = arr;
+#ifdef CONFIRM_COMPILATION_ERRORS
+            CHECK((av.last<6>().bounds() == static_bounds<6>()));
+            CHECK(av.last<6>().length() == 6);
+#endif
+            CHECK_THROW(av.last(6).length(), fail_fast);
+        }
+
+        {
+            span<int, dynamic_range> av;
+            CHECK((av.last<0>().bounds() == static_bounds<0>()));
+            CHECK(av.last<0>().length() == 0);
+            CHECK(av.last(0).length() == 0);
+        }
+    }
+
+    TEST(subspan)
+    {
+        int arr[5] = {1, 2, 3, 4, 5};
+
+        {
+            span<int, 5> av = arr;
+            CHECK((av.subspan<2, 2>().bounds() == static_bounds<2>()));
+            CHECK((av.subspan<2, 2>().length() == 2));
+            CHECK(av.subspan(2, 2).length() == 2);
+            CHECK(av.subspan(2, 3).length() == 3);
+        }
+
+        {
+            span<int, 5> av = arr;
+            CHECK((av.subspan<0, 0>().bounds() == static_bounds<0>()));
+            CHECK((av.subspan<0, 0>().length() == 0));
+            CHECK(av.subspan(0, 0).length() == 0);
+        }
+
+        {
+            span<int, 5> av = arr;
+            CHECK((av.subspan<0, 5>().bounds() == static_bounds<5>()));
+            CHECK((av.subspan<0, 5>().length() == 5));
+            CHECK(av.subspan(0, 5).length() == 5);
+            CHECK_THROW(av.subspan(0, 6).length(), fail_fast);
+            CHECK_THROW(av.subspan(1, 5).length(), fail_fast);
+        }
+
+        {
+            span<int, 5> av = arr;
+            CHECK((av.subspan<5, 0>().bounds() == static_bounds<0>()));
+            CHECK((av.subspan<5, 0>().length() == 0));
+            CHECK(av.subspan(5, 0).length() == 0);
+            CHECK_THROW(av.subspan(6, 0).length(), fail_fast);
+        }
+
+        {
+            span<int, dynamic_range> av;
+            CHECK((av.subspan<0, 0>().bounds() == static_bounds<0>()));
+            CHECK((av.subspan<0, 0>().length() == 0));
+            CHECK(av.subspan(0, 0).length() == 0);
+            CHECK_THROW((av.subspan<1, 0>().length()), fail_fast);
+        }
+
+        {
+            span<int> av;
+            CHECK(av.subspan(0).length() == 0);
+            CHECK_THROW(av.subspan(1).length(), fail_fast);
+        }
+
+        {
+            span<int> av = arr;
+            CHECK(av.subspan(0).length() == 5);
+            CHECK(av.subspan(1).length() == 4);
+            CHECK(av.subspan(4).length() == 1);
+            CHECK(av.subspan(5).length() == 0);
+            CHECK_THROW(av.subspan(6).length(), fail_fast);
+            auto av2 = av.subspan(1);
+            for (int i = 0; i < 4; ++i) CHECK(av2[i] == i + 2);
+        }
+
+        {
+            span<int, 5> av = arr;
+            CHECK(av.subspan(0).length() == 5);
+            CHECK(av.subspan(1).length() == 4);
+            CHECK(av.subspan(4).length() == 1);
+            CHECK(av.subspan(5).length() == 0);
+            CHECK_THROW(av.subspan(6).length(), fail_fast);
+            auto av2 = av.subspan(1);
+            for (int i = 0; i < 4; ++i) CHECK(av2[i] == i + 2);
+        }
+    }
+
+    TEST(rank)
+    {
+        int arr[2] = {1, 2};
+
+        {
+            span<int> s;
+            CHECK(s.rank() == 1);
+        }
+
+        {
+            span<int, 2> s = arr;
+            CHECK(s.rank() == 1);
+        }
+
+        int arr2d[1][1] = {};
+        {
+            span<int, 1, 1> s = arr2d;
+            CHECK(s.rank() == 2);
+        }
+    }
+
+    TEST(extent)
+    {
+        {
+            span<int> s;
+            CHECK(s.extent() == 0);
+            CHECK(s.extent(0) == 0);
+            CHECK_THROW(s.extent(1), fail_fast);
+#ifdef CONFIRM_COMPILATION_ERRORS
+            CHECK(s.extent<1>() == 0);
+#endif
+        }
+
+        {
+            span<int, 0> s;
+            CHECK(s.extent() == 0);
+            CHECK(s.extent(0) == 0);
+            CHECK_THROW(s.extent(1), fail_fast);
+        }
+
+        {
+            int arr2d[1][2] = {};
+
+            span<int, 1, 2> s = arr2d;
+            CHECK(s.extent() == 1);
+            CHECK(s.extent<0>() == 1);
+            CHECK(s.extent<1>() == 2);
+            CHECK(s.extent(0) == 1);
+            CHECK(s.extent(1) == 2);
+            CHECK_THROW(s.extent(3), fail_fast);
+        }
+
+        {
+            int arr2d[1][2] = {};
+
+            span<int, 0, 2> s = arr2d;
+            CHECK(s.extent() == 0);
+            CHECK(s.extent<0>() == 0);
+            CHECK(s.extent<1>() == 2);
+            CHECK(s.extent(0) == 0);
+            CHECK(s.extent(1) == 2);
+            CHECK_THROW(s.extent(3), fail_fast);
+        }
+    }
+
+    TEST(operator_function_call)
+    {
+        int arr[4] = {1, 2, 3, 4};
+
+        {
+            span<int> s = arr;
+            CHECK(s(0) == 1);
+            CHECK_THROW(s(5), fail_fast);
+        }
+
+        int arr2d[2][3] = {1, 2, 3, 4, 5, 6};
+
+        {
+            span<int, 2, 3> s = arr2d;
+            CHECK(s(0, 0) == 1);
+            CHECK(s(1, 2) == 6);
+        }
+    }
+
+    TEST(comparison_operators)
+    {
+        {
+            int arr[10][2];
+            auto s1 = as_span(arr);
+            span<const int, dynamic_range, 2> s2 = s1;
+
+            CHECK(s1 == s2);
+
+            span<int, 20> s3 = as_span(s1, dim<>(20));
+            CHECK(s3 == s2 && s3 == s1);
+        }
+
+        {
+            auto s1 = nullptr;
+            auto s2 = nullptr;
+            CHECK(s1 == s2);
+            CHECK(!(s1 != s2));
+            CHECK(!(s1 < s2));
+            CHECK(s1 <= s2);
+            CHECK(!(s1 > s2));
+            CHECK(s1 >= s2);
+            CHECK(s2 == s1);
+            CHECK(!(s2 != s1));
+            CHECK(!(s2 < s1));
+            CHECK(s2 <= s1);
+            CHECK(!(s2 > s1));
+            CHECK(s2 >= s1);
+        }
+
+        {
+            int arr[] = {2, 1}; // bigger
+
+            span<int> s1 = nullptr;
+            span<int> s2 = arr;
+
+            CHECK(s1 != s2);
+            CHECK(s2 != s1);
+            CHECK(!(s1 == s2));
+            CHECK(!(s2 == s1));
+            CHECK(s1 < s2);
+            CHECK(!(s2 < s1));
+            CHECK(s1 <= s2);
+            CHECK(!(s2 <= s1));
+            CHECK(s2 > s1);
+            CHECK(!(s1 > s2));
+            CHECK(s2 >= s1);
+            CHECK(!(s1 >= s2));
+        }
+
+        {
+            int arr1[] = {1, 2};
+            int arr2[] = {1, 2};
+            span<int> s1 = arr1;
+            span<int> s2 = arr2;
+
+            CHECK(s1 == s2);
+            CHECK(!(s1 != s2));
+            CHECK(!(s1 < s2));
+            CHECK(s1 <= s2);
+            CHECK(!(s1 > s2));
+            CHECK(s1 >= s2);
+            CHECK(s2 == s1);
+            CHECK(!(s2 != s1));
+            CHECK(!(s2 < s1));
+            CHECK(s2 <= s1);
+            CHECK(!(s2 > s1));
+            CHECK(s2 >= s1);
+        }
+
+        {
+            int arr[] = {1, 2, 3};
+
+            span<int> s1 = {&arr[0], 2}; // shorter
+            span<int> s2 = arr; // longer
+
+            CHECK(s1 != s2);
+            CHECK(s2 != s1);
+            CHECK(!(s1 == s2));
+            CHECK(!(s2 == s1));
+            CHECK(s1 < s2);
+            CHECK(!(s2 < s1));
+            CHECK(s1 <= s2);
+            CHECK(!(s2 <= s1));
+            CHECK(s2 > s1);
+            CHECK(!(s1 > s2));
+            CHECK(s2 >= s1);
+            CHECK(!(s1 >= s2));
+        }
+
+        {
+            int arr1[] = {1, 2}; // smaller
+            int arr2[] = {2, 1}; // bigger
+
+            span<int> s1 = arr1;
+            span<int> s2 = arr2;
+
+            CHECK(s1 != s2);
+            CHECK(s2 != s1);
+            CHECK(!(s1 == s2));
+            CHECK(!(s2 == s1));
+            CHECK(s1 < s2);
+            CHECK(!(s2 < s1));
+            CHECK(s1 <= s2);
+            CHECK(!(s2 <= s1));
+            CHECK(s2 > s1);
+            CHECK(!(s1 > s2));
+            CHECK(s2 >= s1);
+            CHECK(!(s1 >= s2));
+        }
+    }
+
+    TEST(basics)
+    {
+        auto ptr = as_span(new int[10], 10);
+        fill(ptr.begin(), ptr.end(), 99);
+        for (int num : ptr) {
+            CHECK(num == 99);
+        }
+
+        delete[] ptr.data();
+    }
+
+    TEST(bounds_checks)
+    {
+        int arr[10][2];
+        auto av = as_span(arr);
+
+        fill(begin(av), end(av), 0);
+
+        av[2][0] = 1;
+        av[1][1] = 3;
+
+        // out of bounds
+        CHECK_THROW(av[1][3] = 3, fail_fast);
+        CHECK_THROW((av[{1, 3}] = 3), fail_fast);
+
+        CHECK_THROW(av[10][2], fail_fast);
+        CHECK_THROW((av[{10, 2}]), fail_fast);
+    }
+
+    void overloaded_func(span<const int, dynamic_range, 3, 5> exp, int expected_value)
+    {
+        for (auto val : exp) {
+            CHECK(val == expected_value);
+        }
+    }
+
+    void overloaded_func(span<const char, dynamic_range, 3, 5> exp, char expected_value)
+    {
+        for (auto val : exp) {
+            CHECK(val == expected_value);
+        }
+    }
+
+    void fixed_func(span<int, 3, 3, 5> exp, int expected_value)
+    {
+        for (auto val : exp) {
+            CHECK(val == expected_value);
+        }
+    }
+
+    TEST(span_parameter_test)
+    {
+        auto data = new int[4][3][5];
+
+        auto av = as_span(data, 4);
+
+        CHECK(av.size() == 60);
+
+        fill(av.begin(), av.end(), 34);
+
+        int count = 0;
+        for_each(av.rbegin(), av.rend(), [&](int val) { count += val; });
+        CHECK(count == 34 * 60);
+        overloaded_func(av, 34);
+
+        overloaded_func(as_span(av, dim<>(4), dim<>(3), dim<>(5)), 34);
+
+        // fixed_func(av, 34);
+        delete[] data;
+    }
+
+    TEST(md_access)
+    {
+        auto width = 5, height = 20;
+
+        auto imgSize = width * height;
+        auto image_ptr = new int[imgSize][3];
+
+        // size check will be done
+        auto image_view =
+            as_span(as_span(image_ptr, imgSize), dim<>(height), dim<>(width), dim<3>());
+
+        iota(image_view.begin(), image_view.end(), 1);
+
+        int expected = 0;
+        for (auto i = 0; i < height; i++) {
+            for (auto j = 0; j < width; j++) {
+                CHECK(expected + 1 == image_view[i][j][0]);
+                CHECK(expected + 2 == image_view[i][j][1]);
+                CHECK(expected + 3 == image_view[i][j][2]);
+
+                auto val = image_view[{i, j, 0}];
+                CHECK(expected + 1 == val);
+                val = image_view[{i, j, 1}];
+                CHECK(expected + 2 == val);
+                val = image_view[{i, j, 2}];
+                CHECK(expected + 3 == val);
+
+                expected += 3;
+            }
+        }
+    }
+
+    TEST(as_span)
+    {
+        {
+            int* arr = new int[150];
+
+            auto av = as_span(arr, dim<10>(), dim<>(3), dim<5>());
+
+            fill(av.begin(), av.end(), 24);
+            overloaded_func(av, 24);
+
+            delete[] arr;
+
+            array<int, 15> stdarr{0};
+            auto av2 = as_span(stdarr);
+            overloaded_func(as_span(av2, dim<>(1), dim<3>(), dim<5>()), 0);
+
+            string str = "ttttttttttttttt"; // size = 15
+            auto t = str.data();
+            (void) t;
+            auto av3 = as_span(str);
+            overloaded_func(as_span(av3, dim<>(1), dim<3>(), dim<5>()), 't');
+        }
+
+        {
+            string str;
+            span<char> strspan = as_span(str);
+            (void) strspan;
+            const string cstr;
+            span<const char> cstrspan = as_span(cstr);
+            (void) cstrspan;
+        }
+
+        {
+            int a[3][4][5];
+            auto av = as_span(a);
+            const int(*b)[4][5];
+            b = a;
+            auto bv = as_span(b, 3);
+
+            CHECK(av == bv);
+
+            const std::array<double, 3> arr = {0.0, 0.0, 0.0};
+            auto cv = as_span(arr);
+            (void) cv;
+
+            vector<float> vec(3);
+            auto dv = as_span(vec);
+            (void) dv;
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+            auto dv2 = as_span(std::move(vec));
+#endif
+        }
+    }
+
+    TEST(empty_spans)
+    {
+        {
+            span<int, 0> empty_av(nullptr);
+
+            CHECK(empty_av.bounds().index_bounds() == index<1>{0});
+            CHECK_THROW(empty_av[0], fail_fast);
+            CHECK_THROW(empty_av.begin()[0], fail_fast);
+            CHECK_THROW(empty_av.cbegin()[0], fail_fast);
+            for (auto& v : empty_av) {
+                (void) v;
+                CHECK(false);
+            }
+        }
+
+        {
+            span<int> empty_av = {};
+            CHECK(empty_av.bounds().index_bounds() == index<1>{0});
+            CHECK_THROW(empty_av[0], fail_fast);
+            CHECK_THROW(empty_av.begin()[0], fail_fast);
+            CHECK_THROW(empty_av.cbegin()[0], fail_fast);
+            for (auto& v : empty_av) {
+                (void) v;
+                CHECK(false);
+            }
+        }
+    }
+
+    TEST(index_constructor)
+    {
+        auto arr = new int[8];
+        for (int i = 0; i < 4; ++i) {
+            arr[2 * i] = 4 + i;
+            arr[2 * i + 1] = i;
+        }
+
+        span<int, dynamic_range> av(arr, 8);
+
+        ptrdiff_t a[1] = {0};
+        index<1> i = a;
+
+        CHECK(av[i] == 4);
+
+        auto av2 = as_span(av, dim<4>(), dim<>(2));
+        ptrdiff_t a2[2] = {0, 1};
+        index<2> i2 = a2;
+
+        CHECK(av2[i2] == 0);
+        CHECK(av2[0][i] == 4);
+
+        delete[] arr;
+    }
+
+    TEST(index_constructors)
+    {
+        {
+            // components of the same type
+            index<3> i1(0, 1, 2);
+            CHECK(i1[0] == 0);
+
+            // components of different types
+            size_t c0 = 0;
+            size_t c1 = 1;
+            index<3> i2(c0, c1, 2);
+            CHECK(i2[0] == 0);
+
+            // from array
+            index<3> i3 = {0, 1, 2};
+            CHECK(i3[0] == 0);
+
+            // from other index of the same size type
+            index<3> i4 = i3;
+            CHECK(i4[0] == 0);
+
+            // default
+            index<3> i7;
+            CHECK(i7[0] == 0);
+
+            // default
+            index<3> i9 = {};
+            CHECK(i9[0] == 0);
+        }
+
+        {
+            // components of the same type
+            index<1> i1(0);
+            CHECK(i1[0] == 0);
+
+            // components of different types
+            size_t c0 = 0;
+            index<1> i2(c0);
+            CHECK(i2[0] == 0);
+
+            // from array
+            index<1> i3 = {0};
+            CHECK(i3[0] == 0);
+
+            // from int
+            index<1> i4 = 0;
+            CHECK(i4[0] == 0);
+
+            // from other index of the same size type
+            index<1> i5 = i3;
+            CHECK(i5[0] == 0);
+
+            // default
+            index<1> i8;
+            CHECK(i8[0] == 0);
+
+            // default
+            index<1> i9 = {};
+            CHECK(i9[0] == 0);
+        }
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+        {
+            index<3> i1(0, 1);
+            index<3> i2(0, 1, 2, 3);
+            index<3> i3 = {0};
+            index<3> i4 = {0, 1, 2, 3};
+            index<1> i5 = {0, 1};
+        }
+#endif
+    }
+
+    TEST(index_operations)
+    {
+        ptrdiff_t a[3] = {0, 1, 2};
+        ptrdiff_t b[3] = {3, 4, 5};
+        index<3> i = a;
+        index<3> j = b;
+
+        CHECK(i[0] == 0);
+        CHECK(i[1] == 1);
+        CHECK(i[2] == 2);
+
+        {
+            index<3> k = i + j;
+
+            CHECK(i[0] == 0);
+            CHECK(i[1] == 1);
+            CHECK(i[2] == 2);
+            CHECK(k[0] == 3);
+            CHECK(k[1] == 5);
+            CHECK(k[2] == 7);
+        }
+
+        {
+            index<3> k = i * 3;
+
+            CHECK(i[0] == 0);
+            CHECK(i[1] == 1);
+            CHECK(i[2] == 2);
+            CHECK(k[0] == 0);
+            CHECK(k[1] == 3);
+            CHECK(k[2] == 6);
+        }
+
+        {
+            index<3> k = 3 * i;
+
+            CHECK(i[0] == 0);
+            CHECK(i[1] == 1);
+            CHECK(i[2] == 2);
+            CHECK(k[0] == 0);
+            CHECK(k[1] == 3);
+            CHECK(k[2] == 6);
+        }
+
+        {
+            index<2> k = details::shift_left(i);
+
+            CHECK(i[0] == 0);
+            CHECK(i[1] == 1);
+            CHECK(i[2] == 2);
+            CHECK(k[0] == 1);
+            CHECK(k[1] == 2);
+        }
+    }
+
+    void iterate_second_column(span<int, dynamic_range, dynamic_range> av)
+    {
+        auto length = av.size() / 2;
+
+        // view to the second column
+        auto section = av.section({0, 1}, {length, 1});
+
+        CHECK(section.size() == length);
+        for (auto i = 0; i < section.size(); ++i) {
+            CHECK(section[i][0] == av[i][1]);
+        }
+
+        for (auto i = 0; i < section.size(); ++i) {
+            auto idx = index<2>{i, 0}; // avoid braces inside the CHECK macro
+            CHECK(section[idx] == av[i][1]);
+        }
+
+        CHECK(section.bounds().index_bounds()[0] == length);
+        CHECK(section.bounds().index_bounds()[1] == 1);
+        for (auto i = 0; i < section.bounds().index_bounds()[0]; ++i) {
+            for (auto j = 0; j < section.bounds().index_bounds()[1]; ++j) {
+                auto idx = index<2>{i, j}; // avoid braces inside the CHECK macro
+                CHECK(section[idx] == av[i][1]);
+            }
+        }
+
+        size_t check_sum = 0;
+        for (auto i = 0; i < length; ++i) {
+            check_sum += av[i][1];
+        }
+
+        {
+            auto idx = 0;
+            size_t sum = 0;
+            for (auto num : section) {
+                CHECK(num == av[idx][1]);
+                sum += num;
+                idx++;
+            }
+
+            CHECK(sum == check_sum);
+        }
+        {
+            size_t idx = length - 1;
+            size_t sum = 0;
+            for (auto iter = section.rbegin(); iter != section.rend(); ++iter) {
+                CHECK(*iter == av[idx][1]);
+                sum += *iter;
+                idx--;
+            }
+
+            CHECK(sum == check_sum);
+        }
+    }
+
+    TEST(span_section_iteration)
+    {
+        int arr[4][2] = {{4, 0}, {5, 1}, {6, 2}, {7, 3}};
+
+        // static bounds
+        {
+            span<int, 4, 2> av = arr;
+            iterate_second_column(av);
+        }
+        // first bound is dynamic
+        {
+            span<int, dynamic_range, 2> av = arr;
+            iterate_second_column(av);
+        }
+        // second bound is dynamic
+        {
+            span<int, 4, dynamic_range> av = arr;
+            iterate_second_column(av);
+        }
+        // both bounds are dynamic
+        {
+            span<int, dynamic_range, dynamic_range> av = arr;
+            iterate_second_column(av);
+        }
+    }
+
+    TEST(dynamic_span_section_iteration)
+    {
+        auto height = 4, width = 2;
+        auto size = height * width;
+
+        auto arr = new int[size];
+        for (auto i = 0; i < size; ++i) {
+            arr[i] = i;
+        }
+
+        auto av = as_span(arr, size);
+
+        // first bound is dynamic
+        {
+            span<int, dynamic_range, 2> av2 = as_span(av, dim<>(height), dim<>(width));
+            iterate_second_column(av2);
+        }
+        // second bound is dynamic
+        {
+            span<int, 4, dynamic_range> av2 = as_span(av, dim<>(height), dim<>(width));
+            iterate_second_column(av2);
+        }
+        // both bounds are dynamic
+        {
+            span<int, dynamic_range, dynamic_range> av2 = as_span(av, dim<>(height), dim<>(width));
+            iterate_second_column(av2);
+        }
+
+        delete[] arr;
+    }
+
+    TEST(span_structure_size)
+    {
+        double(*arr)[3][4] = new double[100][3][4];
+        span<double, dynamic_range, 3, 4> av1(arr, 10);
+
+        struct EffectiveStructure
+        {
+            double* v1;
+            ptrdiff_t v2;
+        };
+        CHECK(sizeof(av1) == sizeof(EffectiveStructure));
+
+        CHECK_THROW(av1[10][3][4], fail_fast);
+
+        span<const double, dynamic_range, 6, 4> av2 = as_span(av1, dim<>(5), dim<6>(), dim<4>());
+        (void) av2;
+    }
+
+    TEST(fixed_size_conversions)
+    {
+        int arr[] = {1, 2, 3, 4};
+
+        // converting to an span from an equal size array is ok
+        span<int, 4> av4 = arr;
+        CHECK(av4.length() == 4);
+
+        // converting to dynamic_range a_v is always ok
+        {
+            span<int, dynamic_range> av = av4;
+            (void) av;
+        }
+        {
+            span<int, dynamic_range> av = arr;
+            (void) av;
+        }
+
+// initialization or assignment to static span that REDUCES size is NOT ok
+#ifdef CONFIRM_COMPILATION_ERRORS
+        {
+            span<int, 2> av2 = arr;
+        }
+        {
+            span<int, 2> av2 = av4;
+        }
+#endif
+
+        {
+            span<int, dynamic_range> av = arr;
+            span<int, 2> av2 = av;
+            (void) av2;
+        }
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+        {
+            span<int, dynamic_range> av = arr;
+            span<int, 2, 1> av2 = av.as_span(dim<2>(), dim<2>());
+        }
+#endif
+
+        {
+            span<int, dynamic_range> av = arr;
+            span<int, 2, 1> av2 = as_span(av, dim<>(2), dim<>(2));
+            auto workaround_macro = [&]() { return av2[{1, 0}] == 2; };
+            CHECK(workaround_macro());
+        }
+
+        // but doing so explicitly is ok
+
+        // you can convert statically
+        {
+            span<int, 2> av2 = {arr, 2};
+            (void) av2;
+        }
+        {
+            span<int, 1> av2 = av4.first<1>();
+            (void) av2;
+        }
+
+        // ...or dynamically
+        {
+            // NB: implicit conversion to span<int,2> from span<int,dynamic_range>
+            span<int, 1> av2 = av4.first(1);
+            (void) av2;
+        }
+
+        // initialization or assignment to static span that requires size INCREASE is not ok.
+        int arr2[2] = {1, 2};
+
+#ifdef CONFIRM_COMPILATION_ERRORS
+        {
+            span<int, 4> av4 = arr2;
+        }
+        {
+            span<int, 2> av2 = arr2;
+            span<int, 4> av4 = av2;
+        }
+#endif
+        {
+            auto f = [&]() {
+                span<int, 4> av9 = {arr2, 2};
+                (void) av9;
+            };
+            CHECK_THROW(f(), fail_fast);
+        }
+
+        // this should fail - we are trying to assign a small dynamic a_v to a fixed_size larger one
+        span<int, dynamic_range> av = arr2;
+        auto f = [&]() {
+            span<int, 4> av2 = av;
+            (void) av2;
+        };
+        CHECK_THROW(f(), fail_fast);
+    }
+
+    TEST(as_writeable_bytes)
+    {
+        int a[] = {1, 2, 3, 4};
+
+        {
+#ifdef CONFIRM_COMPILATION_ERRORS
+            // you should not be able to get writeable bytes for const objects
+            span<const int, dynamic_range> av = a;
+            auto wav = av.as_writeable_bytes();
+#endif
+        }
+
+        {
+            span<int, dynamic_range> av;
+            auto wav = as_writeable_bytes(av);
+            CHECK(wav.length() == av.length());
+            CHECK(wav.length() == 0);
+            CHECK(wav.size_bytes() == 0);
+        }
+
+        {
+            span<int, dynamic_range> av = a;
+            auto wav = as_writeable_bytes(av);
+            CHECK(wav.data() == (byte*) &a[0]);
+            CHECK(wav.length() == sizeof(a));
+        }
+    }
+
+    TEST(iterator)
+    {
+        int a[] = {1, 2, 3, 4};
+
+        {
+            span<int, dynamic_range> av = a;
+            auto wav = as_writeable_bytes(av);
+            for (auto& b : wav) {
+                b = byte(0);
+            }
+            for (size_t i = 0; i < 4; ++i) {
+                CHECK(a[i] == 0);
+            }
+        }
+
+        {
+            span<int, dynamic_range> av = a;
+            for (auto& n : av) {
+                n = 1;
+            }
+            for (size_t i = 0; i < 4; ++i) {
+                CHECK(a[i] == 1);
+            }
+        }
+    }
+#endif    
+}
+
+int main(int, const char* []) { return UnitTest::RunAllTests(); }