text: ///////////////////////////////////////////////////////////////////////////////
  //
  // 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.
  //
  ///////////////////////////////////////////////////////////////////////////////
  
  #ifdef _MSC_VER
  // blanket turn off warnings from CppCoreCheck from catch
  // so people aren't annoyed by them when running the tool.
  #pragma warning(disable : 26440 26426 26497) // from catch
  
  #endif
  
  #include <catch/catch.hpp> // for AssertionHandler, StringRef, CHECK, TEST_...
  
  #include <gsl/gsl_byte> // for byte
  #include <gsl/gsl_util> // for narrow_cast, at
  #include <gsl/span>     // for span, span_iterator, operator==, operator!=
  
  #include <array>       // for array
  #include <iostream>    // for ptrdiff_t
  #include <iterator>    // for reverse_iterator, operator-, operator==
  #include <memory>      // for unique_ptr, shared_ptr, make_unique, allo...
  #include <regex>       // for match_results, sub_match, match_results<>...
  #include <stddef.h>    // for ptrdiff_t
  #include <string>      // for string
  #include <type_traits> // for integral_constant<>::value, is_default_co...
  #include <vector>      // for vector
  
  namespace gsl
  {
  struct fail_fast;
  } // namespace gsl
  
  using namespace std;
  using namespace gsl;
  
  namespace
  {
  struct BaseClass
  {
  };
  struct DerivedClass : BaseClass
  {
  };
  struct AddressOverloaded
  {
  #if (__cplusplus > 201402L)
      [[maybe_unused]]
  #endif
      AddressOverloaded operator&() const { return {}; }
  };
  } // namespace
  
  GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
  TEST_CASE("default_constructor")
  {
      {
          span<int> s;
          CHECK((s.size() == 0 && s.data() == nullptr));
  
          span<const int> cs;
          CHECK((cs.size() == 0 && cs.data() == nullptr));
      }
  
      {
          span<int, 0> s;
          CHECK((s.size() == 0 && s.data() == nullptr));
  
          span<const int, 0> cs;
          CHECK((cs.size() == 0 && cs.data() == nullptr));
      }
  
      {
  #ifdef CONFIRM_COMPILATION_ERRORS
          span<int, 1> s;
          CHECK((s.size() == 1 && s.data() == nullptr)); // explains why it can't compile
  #endif
      }
  
      {
          span<int> s{};
          CHECK((s.size() == 0 && s.data() == nullptr));
  
          span<const int> cs{};
          CHECK((cs.size() == 0 && cs.data() == nullptr));
      }
  }
  
  GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
  TEST_CASE("size_optimization")
  {
      {
          span<int> s;
          CHECK(sizeof(s) == sizeof(int*) + sizeof(ptrdiff_t));
      }
  
      {
          span<int, 0> s;
          CHECK(sizeof(s) == sizeof(int*));
      }
  }
  
  GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
  TEST_CASE("from_nullptr_size_constructor")
  {
      {
          span<int> s{nullptr, narrow_cast<span<int>::index_type>(0)};
          CHECK((s.size() == 0 && s.data() == nullptr));
  
          span<const int> cs{nullptr, narrow_cast<span<int>::index_type>(0)};
          CHECK((cs.size() == 0 && cs.data() == nullptr));
      }
  
      {
          span<int, 0> s{nullptr, narrow_cast<span<int>::index_type>(0)};
          CHECK((s.size() == 0 && s.data() == nullptr));
  
          span<const int, 0> cs{nullptr, narrow_cast<span<int>::index_type>(0)};
          CHECK((cs.size() == 0 && cs.data() == nullptr));
      }
  
      {
          auto workaround_macro = []() {
              const span<int, 1> s{nullptr, narrow_cast<span<int>::index_type>(0)};
          };
          CHECK_THROWS_AS(workaround_macro(), fail_fast);
      }
  
      {
          auto workaround_macro = []() { const span<int> s{nullptr, 1}; };
          CHECK_THROWS_AS(workaround_macro(), fail_fast);
  
          auto const_workaround_macro = []() { const span<const int> cs{nullptr, 1}; };
          CHECK_THROWS_AS(const_workaround_macro(), fail_fast);
      }
  
      {
          auto workaround_macro = []() { const span<int, 0> s{nullptr, 1}; };
          CHECK_THROWS_AS(workaround_macro(), fail_fast);
  
          auto const_workaround_macro = []() { const span<const int, 0> s{nullptr, 1}; };
          CHECK_THROWS_AS(const_workaround_macro(), fail_fast);
      }
  
      {
          span<int*> s{nullptr, narrow_cast<span<int>::index_type>(0)};
          CHECK((s.size() == 0 && s.data() == nullptr));
  
          span<const int*> cs{nullptr, narrow_cast<span<int>::index_type>(0)};
          CHECK((cs.size() == 0 && cs.data() == nullptr));
      }
  }
  
  GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
  GSL_SUPPRESS(bounds.4) // NO-FORMAT: attribute
  GSL_SUPPRESS(bounds.2) // NO-FORMAT: attribute
  TEST_CASE("from_pointer_length_constructor")
  {
      int arr[4] = {1, 2, 3, 4};
  
      {
          for(int i = 0; i<4 ; ++i)
          {
              {
                  span<int> s = { &arr[0], i };
                  CHECK(s.size() == i);
                  CHECK(s.data() == &arr[0]);
                  CHECK(s.empty() == (i == 0));
                  for (int j = 0; j < i; ++j)
                  {
                      CHECK(arr[j] == s[j]);
                      CHECK(arr[j] == s.at(j));
                      CHECK(arr[j] == s(j));
                  }
              }
              {
                  span<int> s = { &arr[i], 4-narrow_cast<ptrdiff_t>(i) };
                  CHECK(s.size() == 4-i);
                  CHECK(s.data() == &arr[i]);
                  CHECK(s.empty() == (4-i == 0));
                  for (int j = 0; j < 4-i; ++j)
                  {
                      CHECK(arr[j+i] == s[j]);
                      CHECK(arr[j+i] == s.at(j));
                      CHECK(arr[j+i] == s(j));
                  }
              }
          }
      }
  
      {
          span<int, 2> s{&arr[0], 2};
          CHECK((s.size() == 2 && s.data() == &arr[0]));
          CHECK((s[0] == 1 && s[1] == 2));
      }
  
      {
          int* p = nullptr;
          span<int> s{p, narrow_cast<span<int>::index_type>(0)};
          CHECK((s.size() == 0 && s.data() == nullptr));
      }
  
      {
          int* p = nullptr;
          auto workaround_macro = [=]() { const span<int> s{p, 2}; };
          CHECK_THROWS_AS(workaround_macro(), fail_fast);
      }
  
      {
          auto s = make_span(&arr[0], 2);
          CHECK((s.size() == 2 && s.data() == &arr[0]));
          CHECK((s[0] == 1 && s[1] == 2));
      }
  
      {
          int* p = nullptr;
          auto s = make_span(p, narrow_cast<span<int>::index_type>(0));
          CHECK((s.size() == 0 && s.data() == nullptr));
      }
  
      {
          int* p = nullptr;
          auto workaround_macro = [=]() { make_span(p, 2); };
          CHECK_THROWS_AS(workaround_macro(), fail_fast);
      }
  }
  
  
  GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
  TEST_CASE("from_pointer_pointer_constructor")
  {
      int arr[4] = {1, 2, 3, 4};
  
      {
          span<int> s{&arr[0], &arr[2]};
          CHECK((s.size() == 2 && s.data() == &arr[0]));
          CHECK((s[0] == 1 && s[1] == 2));
      }
  
      {
          span<int, 2> s{&arr[0], &arr[2]};
          CHECK((s.size() == 2 && s.data() == &arr[0]));
          CHECK((s[0] == 1 && s[1] == 2));
      }
  
      {
          span<int> s{&arr[0], &arr[0]};
          CHECK((s.size() == 0 && s.data() == &arr[0]));
      }
  
      {
          span<int, 0> s{&arr[0], &arr[0]};
          CHECK((s.size() == 0 && s.data() == &arr[0]));
      }
  
      // this will fail the std::distance() precondition, which asserts on MSVC debug builds
      //{
      //    auto workaround_macro = [&]() { span<int> s{&arr[1], &arr[0]}; };
      //    CHECK_THROWS_AS(workaround_macro(), fail_fast);
      //}
  
      // this will fail the std::distance() precondition, which asserts on MSVC debug builds
      //{
      //    int* p = nullptr;
      //    auto workaround_macro = [&]() { span<int> s{&arr[0], p}; };
      //    CHECK_THROWS_AS(workaround_macro(), fail_fast);
      //}
  
      {
          int* p = nullptr;
          span<int> s{p, p};
          CHECK((s.size() == 0 && s.data() == nullptr));
      }
  
      {
          int* p = nullptr;
          span<int, 0> s{p, p};
          CHECK((s.size() == 0 && s.data() == nullptr));
      }
  
      // this will fail the std::distance() precondition, which asserts on MSVC debug builds
      //{
      //    int* p = nullptr;
      //    auto workaround_macro = [&]() { span<int> s{&arr[0], p}; };
      //    CHECK_THROWS_AS(workaround_macro(), fail_fast);
      //}
  
      {
          auto s = make_span(&arr[0], &arr[2]);
          CHECK((s.size() == 2 && s.data() == &arr[0]));
          CHECK((s[0] == 1 && s[1] == 2));
      }
  
      {
          auto s = make_span(&arr[0], &arr[0]);
          CHECK((s.size() == 0 && s.data() == &arr[0]));
      }
  
      {
          int* p = nullptr;
          auto s = make_span(p, p);
          CHECK((s.size() == 0 && s.data() == nullptr));
      }
  }
  
  TEST_CASE("from_array_constructor")
  {
      int arr[5] = {1, 2, 3, 4, 5};
  
      {
          const span<int> s{arr};
          CHECK((s.size() == 5 && s.data() == &arr[0]));
      }
  
      {
          const span<int, 5> s{arr};
          CHECK((s.size() == 5 && s.data() == &arr[0]));
      }
  
      int arr2d[2][3] = {1, 2, 3, 4, 5, 6};
  
  #ifdef CONFIRM_COMPILATION_ERRORS
      {
          span<int, 6> s{arr};
      }
  
      {
          span<int, 0> s{arr};
          CHECK((s.size() == 0 && s.data() == &arr[0]));
      }
  
      {
          span<int> s{arr2d};
          CHECK((s.size() == 6 && s.data() == &arr2d[0][0]));
          CHECK((s[0] == 1 && s[5] == 6));
      }
  
      {
          span<int, 0> s{arr2d};
          CHECK((s.size() == 0 && s.data() == &arr2d[0][0]));
      }
  
      {
          span<int, 6> s{arr2d};
      }
  #endif
      {
          const span<int[3]> s{std::addressof(arr2d[0]), 1};
          CHECK((s.size() == 1 && s.data() == std::addressof(arr2d[0])));
      }
  
      int arr3d[2][3][2] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12};
  
  #ifdef CONFIRM_COMPILATION_ERRORS
      {
          span<int> s{arr3d};
          CHECK((s.size() == 12 && s.data() == &arr3d[0][0][0]));
          CHECK((s[0] == 1 && s[11] == 12));
      }
  
      {
          span<int, 0> s{arr3d};
          CHECK((s.size() == 0 && s.data() == &arr3d[0][0][0]));
      }
  
      {
          span<int, 11> s{arr3d};
      }
  
      {
          span<int, 12> s{arr3d};
          CHECK((s.size() == 12 && s.data() == &arr3d[0][0][0]));
          CHECK((s[0] == 1 && s[5] == 6));
      }
  #endif
      {
          const span<int[3][2]> s{std::addressof(arr3d[0]), 1};
          CHECK((s.size() == 1 && s.data() == std::addressof(arr3d[0])));
      }
  
      {
          const auto s = make_span(arr);
          CHECK((s.size() == 5 && s.data() == std::addressof(arr[0])));
      }
  
      {
          const auto s = make_span(std::addressof(arr2d[0]), 1);
          CHECK((s.size() == 1 && s.data() == std::addressof(arr2d[0])));
      }
  
      {
          const auto s = make_span(std::addressof(arr3d[0]), 1);
          CHECK((s.size() == 1 && s.data() == std::addressof(arr3d[0])));
      }
  
      AddressOverloaded ao_arr[5] = {};
  
      {
          const span<AddressOverloaded, 5> s{ao_arr};
          CHECK((s.size() == 5 && s.data() == std::addressof(ao_arr[0])));
      }
  
  }
  
  GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
  GSL_SUPPRESS(r.11) // NO-FORMAT: attribute
  GSL_SUPPRESS(i.11) // NO-FORMAT: attribute
  GSL_SUPPRESS(bounds.1) // NO-FORMAT: attribute
  TEST_CASE("from_dynamic_array_constructor")
  {
      double(*arr)[3][4] = new double[100][3][4];
  
      {
          span<double> s(&arr[0][0][0], 10);
          CHECK((s.size() == 10 && s.data() == &arr[0][0][0]));
      }
  
      {
          auto s = make_span(&arr[0][0][0], 10);
          CHECK((s.size() == 10 && s.data() == &arr[0][0][0]));
      }
  
      delete[] arr;
  }
  
  
  GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
  TEST_CASE("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()));
      }
  
      {
          std::array<int, 0> empty_arr{};
          span<int> s{empty_arr};
          CHECK((s.size() == 0 && s.empty()));
      }
  
      std::array<AddressOverloaded, 4> ao_arr{};
  
      {
          span<AddressOverloaded, 4> fs{ao_arr};
          CHECK((fs.size() == narrow_cast<ptrdiff_t>(ao_arr.size()) && ao_arr.data() == fs.data()));
      }
  
  #ifdef CONFIRM_COMPILATION_ERRORS
      {
          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()));
      }
  
      {
          span<int, 5> s{arr};
      }
  
      {
          auto get_an_array = []() -> std::array<int, 4> { return {1, 2, 3, 4}; };
          auto take_a_span = [](span<int> s) { static_cast<void>(s); };
          // try to take a temporary std::array
          take_a_span(get_an_array());
      }
  #endif
  
      {
          auto get_an_array = []() -> std::array<int, 4> { return {1, 2, 3, 4}; };
          auto take_a_span = [](span<const int> s) { static_cast<void>(s); };
          // try to take a temporary std::array
          take_a_span(get_an_array());
      }
  
      {
          auto s = make_span(arr);
          CHECK((s.size() == narrow_cast<ptrdiff_t>(arr.size()) && 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
          CHECK(s1.size() == 4);
          CHECK(s2.size() == 0);
      #else
          CHECK(s1.size() == s2.size());
      #endif
      }
  }
  
  GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
  TEST_CASE("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()));
      }
  
      const std::array<AddressOverloaded, 4> ao_arr{};
  
      {
          span<const AddressOverloaded, 4> s{ao_arr};
          CHECK((s.size() == narrow_cast<ptrdiff_t>(ao_arr.size()) && s.data() == ao_arr.data()));
      }
  
  #ifdef CONFIRM_COMPILATION_ERRORS
      {
          span<const int, 2> s{arr};
          CHECK((s.size() == 2 && s.data() == arr.data()));
      }
  
      {
          span<const int, 0> s{arr};
          CHECK((s.size() == 0 && s.data() == arr.data()));
      }
  
      {
          span<const int, 5> s{arr};
      }
  #endif
  
      {
          auto get_an_array = []() -> const std::array<int, 4> { return {1, 2, 3, 4}; };
          auto take_a_span = [](span<const int> s) { static_cast<void>(s); };
          // try to take a temporary std::array
          take_a_span(get_an_array());
      }
  
      {
          auto s = make_span(arr);
          CHECK((s.size() == narrow_cast<ptrdiff_t>(arr.size()) && s.data() == arr.data()));
      }
  }
  
  GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
  TEST_CASE("from_std_array_const_constructor")
  {
      std::array<const int, 4> arr = {1, 2, 3, 4};
  
      {
          span<const int> s{arr};
          CHECK((s.size() == narrow_cast<ptrdiff_t>(arr.size()) && s.data() == arr.data()));
      }
  
      {
          span<const int, 4> s{arr};
          CHECK((s.size() == narrow_cast<ptrdiff_t>(arr.size()) && s.data() == arr.data()));
      }
  
  #ifdef CONFIRM_COMPILATION_ERRORS
      {
          span<const int, 2> s{arr};
          CHECK((s.size() == 2 && s.data() == arr.data()));
      }
  
      {
          span<const int, 0> s{arr};
          CHECK((s.size() == 0 && s.data() == arr.data()));
      }
  
      {
          span<const int, 5> s{arr};
      }
  
      {
          span<int, 4> s{arr};
      }
  #endif
  
      {
          auto s = make_span(arr);
          CHECK((s.size() == narrow_cast<ptrdiff_t>(arr.size()) && s.data() == arr.data()));
      }
  }
  
  GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
  TEST_CASE("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) { static_cast<void>(s); };
          use_span(get_temp_vector());
  #endif
      }
  
      {
          auto get_temp_vector = []() -> std::vector<int> { return {}; };
          auto use_span = [](span<const int> s) { static_cast<void>(s); };
          use_span(get_temp_vector());
      }
  
      {
  #ifdef CONFIRM_COMPILATION_ERRORS
          auto get_temp_string = []() -> std::string { return {}; };
          auto use_span = [](span<char> s) { static_cast<void>(s); };
          use_span(get_temp_string());
  #endif
      }
  
      {
          auto get_temp_string = []() -> std::string { return {}; };
          auto use_span = [](span<const char> s) { static_cast<void>(s); };
          use_span(get_temp_string());
      }
  
      {
  #ifdef CONFIRM_COMPILATION_ERRORS
          auto get_temp_vector = []() -> const std::vector<int> { return {}; };
          auto use_span = [](span<const char> s) { static_cast<void>(s); };
          use_span(get_temp_vector());
  #endif
      }
  
      {
          auto get_temp_string = []() -> const std::string { return {}; };
          auto use_span = [](span<const char> s) { static_cast<void>(s); };
          use_span(get_temp_string());
      }
  
      {
  #ifdef CONFIRM_COMPILATION_ERRORS
          std::map<int, int> m;
          span<int> s{m};
  #endif
      }
  
      {
          auto s = make_span(v);
          CHECK((s.size() == narrow_cast<std::ptrdiff_t>(v.size()) && s.data() == v.data()));
  
          auto cs = make_span(cv);
          CHECK((cs.size() == narrow_cast<std::ptrdiff_t>(cv.size()) && cs.data() == cv.data()));
      }
  }
  
  GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
  TEST_CASE("from_convertible_span_constructor")
  {
      {
          span<DerivedClass> avd;
          span<const DerivedClass> avcd = avd;
          static_cast<void>(avcd);
      }
  
      {
      #ifdef CONFIRM_COMPILATION_ERRORS
          span<DerivedClass> avd;
          span<BaseClass> avb = avd;
          static_cast<void>(avb);
      #endif
      }
  
      #ifdef CONFIRM_COMPILATION_ERRORS
      {
          span<int> s;
          span<unsigned int> s2 = s;
          static_cast<void>(s2);
      }
  
      {
          span<int> s;
          span<const unsigned int> s2 = s;
          static_cast<void>(s2);
      }
  
      {
          span<int> s;
          span<short> s2 = s;
          static_cast<void>(s2);
      }
      #endif
  }
  
  GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
  TEST_CASE("copy_move_and_assignment")
  {
      span<int> s1;
      CHECK(s1.empty());
  
      int arr[] = {3, 4, 5};
  
      span<const int> s2 = arr;
      CHECK((s2.size() == 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.size() == 2 && s.data() == &arr[1])); };
      use_span(get_temp_span());
  
      s1 = get_temp_span();
      CHECK((s1.size() == 2 && s1.data() == &arr[1]));
  }
  
  GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
  TEST_CASE("first")
  {
      int arr[5] = {1, 2, 3, 4, 5};
  
      {
          span<int, 5> av = arr;
          CHECK(av.first<2>().size() == 2);
          CHECK(av.first(2).size() == 2);
      }
  
      {
          span<int, 5> av = arr;
          CHECK(av.first<0>().size() == 0);
          CHECK(av.first(0).size() == 0);
      }
  
      {
          span<int, 5> av = arr;
          CHECK(av.first<5>().size() == 5);
          CHECK(av.first(5).size() == 5);
      }
  
      {
          span<int, 5> av = arr;
  #ifdef CONFIRM_COMPILATION_ERRORS
          CHECK(av.first<6>().size() == 6);
          CHECK(av.first<-1>().size() == -1);
  #endif
          CHECK_THROWS_AS(av.first(6).size(), fail_fast);
      }
  
      {
          span<int> av;
          CHECK(av.first<0>().size() == 0);
          CHECK(av.first(0).size() == 0);
      }
  }
  
  GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
  TEST_CASE("last")
  {
      int arr[5] = {1, 2, 3, 4, 5};
  
      {
          span<int, 5> av = arr;
          CHECK(av.last<2>().size() == 2);
          CHECK(av.last(2).size() == 2);
      }
  
      {
          span<int, 5> av = arr;
          CHECK(av.last<0>().size() == 0);
          CHECK(av.last(0).size() == 0);
      }
  
      {
          span<int, 5> av = arr;
          CHECK(av.last<5>().size() == 5);
          CHECK(av.last(5).size() == 5);
      }
  
      {
          span<int, 5> av = arr;
  #ifdef CONFIRM_COMPILATION_ERRORS
          CHECK(av.last<6>().size() == 6);
  #endif
          CHECK_THROWS_AS(av.last(6).size(), fail_fast);
      }
  
      {
          span<int> av;
          CHECK(av.last<0>().size() == 0);
          CHECK(av.last(0).size() == 0);
      }
  }
  
  GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
  TEST_CASE("subspan")
  {
      int arr[5] = {1, 2, 3, 4, 5};
  
      {
          span<int, 5> av = arr;
          CHECK((av.subspan<2, 2>().size() == 2));
          CHECK(decltype(av.subspan<2, 2>())::extent == 2);
          CHECK(av.subspan(2, 2).size() == 2);
          CHECK(av.subspan(2, 3).size() == 3);
      }
  
      {
          span<int, 5> av = arr;
          CHECK((av.subspan<0, 0>().size() == 0));
          CHECK(decltype(av.subspan<0,0>())::extent == 0);
          CHECK(av.subspan(0, 0).size() == 0);
      }
  
      {
          span<int, 5> av = arr;
          CHECK((av.subspan<0, 5>().size() == 5));
          CHECK(decltype(av.subspan<0, 5>())::extent == 5);
          CHECK(av.subspan(0, 5).size() == 5);
  
          CHECK_THROWS_AS(av.subspan(0, 6).size(), fail_fast);
          CHECK_THROWS_AS(av.subspan(1, 5).size(), fail_fast);
      }
  
      {
          span<int, 5> av = arr;
          CHECK((av.subspan<4, 0>().size() == 0));
          CHECK(decltype(av.subspan<4, 0>())::extent == 0);
          CHECK(av.subspan(4, 0).size() == 0);
          CHECK(av.subspan(5, 0).size() == 0);
          CHECK_THROWS_AS(av.subspan(6, 0).size(), fail_fast);
      }
  
      {
          span<int, 5> av = arr;
          CHECK((av.subspan<1>().size() == 4));
          CHECK(decltype(av.subspan<1>())::extent == 4);    
      }
  
      {
          span<int> av;
          CHECK((av.subspan<0, 0>().size() == 0));
          CHECK((decltype(av.subspan<0, 0>())::extent == 0));
          CHECK(av.subspan(0, 0).size() == 0);
          CHECK_THROWS_AS((av.subspan<1, 0>().size()), fail_fast);
      }
  
      {
          span<int> av;
          CHECK(av.subspan(0).size() == 0);
          CHECK_THROWS_AS(av.subspan(1).size(), fail_fast);
      }
  
      {
          span<int> av = arr;
          CHECK(av.subspan(0).size() == 5);
          CHECK(av.subspan(1).size() == 4);
          CHECK(av.subspan(4).size() == 1);
          CHECK(av.subspan(5).size() == 0);
          CHECK_THROWS_AS(av.subspan(6).size(), fail_fast);
          const 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).size() == 5);
          CHECK(av.subspan(1).size() == 4);
          CHECK(av.subspan(4).size() == 1);
          CHECK(av.subspan(5).size() == 0);
          CHECK_THROWS_AS(av.subspan(6).size(), fail_fast);
          const auto av2 = av.subspan(1);
          for (int i = 0; i < 4; ++i) CHECK(av2[i] == i + 2);
      }
  }
  
  GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
  TEST_CASE("at_call")
  {
      int arr[4] = {1, 2, 3, 4};
  
      {
          span<int> s = arr;
          CHECK(s.at(0) == 1);
          CHECK_THROWS_AS(s.at(5), fail_fast);
      }
  
      {
          int arr2d[2] = {1, 6};
          span<int, 2> s = arr2d;
          CHECK(s.at(0) == 1);
          CHECK(s.at(1) == 6);
          CHECK_THROWS_AS(s.at(2), fail_fast);
      }
  }
  
  GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
  TEST_CASE("operator_function_call")
  {
      int arr[4] = {1, 2, 3, 4};
  
      {
          span<int> s = arr;
          CHECK(s(0) == 1);
          CHECK_THROWS_AS(s(5), fail_fast);
      }
  
      {
          int arr2d[2] = {1, 6};
          span<int, 2> s = arr2d;
          CHECK(s(0) == 1);
          CHECK(s(1) == 6);
          CHECK_THROWS_AS(s(2), fail_fast);
      }
  }
  
  GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
  TEST_CASE("iterator_default_init")
  {
      span<int>::iterator it1;
      span<int>::iterator it2;
      CHECK(it1 == it2);
  }
  
  GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
  TEST_CASE("const_iterator_default_init")
  {
      span<int>::const_iterator it1;
      span<int>::const_iterator it2;
      CHECK(it1 == it2);
  }
  
  GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
  TEST_CASE("iterator_conversions")
  {
      span<int>::iterator badIt;
      span<int>::const_iterator badConstIt;
      CHECK(badIt == badConstIt);
  
      int a[] = {1, 2, 3, 4};
      span<int> s = a;
  
      auto it = s.begin();
      auto cit = s.cbegin();
  
      CHECK(it == cit);
      CHECK(cit == it);
  
      span<int>::const_iterator cit2 = it;
      CHECK(cit2 == cit);
  
      span<int>::const_iterator cit3 = it + 4;
      CHECK(cit3 == s.cend());
  }
  
  GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
  TEST_CASE("iterator_comparisons")
  {
      int a[] = {1, 2, 3, 4};
      {
          span<int> s = a;
          span<int>::iterator it = s.begin();
          auto it2 = it + 1;
          span<int>::const_iterator cit = s.cbegin();
  
          CHECK(it == cit);
          CHECK(cit == it);
          CHECK(it == it);
          CHECK(cit == cit);
          CHECK(cit == s.begin());
          CHECK(s.begin() == cit);
          CHECK(s.cbegin() == cit);
          CHECK(it == s.begin());
          CHECK(s.begin() == it);
  
          CHECK(it != it2);
          CHECK(it2 != it);
          CHECK(it != s.end());
          CHECK(it2 != s.end());
          CHECK(s.end() != it);
          CHECK(it2 != cit);
          CHECK(cit != it2);
  
          CHECK(it < it2);
          CHECK(it <= it2);
          CHECK(it2 <= s.end());
          CHECK(it < s.end());
          CHECK(it <= cit);
          CHECK(cit <= it);
          CHECK(cit < it2);
          CHECK(cit <= it2);
          CHECK(cit < s.end());
          CHECK(cit <= s.end());
  
          CHECK(it2 > it);
          CHECK(it2 >= it);
          CHECK(s.end() > it2);
          CHECK(s.end() >= it2);
          CHECK(it2 > cit);
          CHECK(it2 >= cit);
      }
  }
  
  GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
  TEST_CASE("begin_end")
  {
      {
          int a[] = {1, 2, 3, 4};
          span<int> s = a;
  
          span<int>::iterator it = s.begin();
          span<int>::iterator it2 = std::begin(s);
          CHECK(it == it2);
  
          it = s.end();
          it2 = std::end(s);
          CHECK(it == it2);
      }
  
      {
          int a[] = {1, 2, 3, 4};
          span<int> s = a;
  
          auto it = s.begin();
          auto first = it;
          CHECK(it == first);
          CHECK(*it == 1);
  
          auto beyond = s.end();
          CHECK(it != beyond);
          CHECK_THROWS_AS(*beyond, fail_fast);
  
          CHECK(beyond - first == 4);
          CHECK(first - first == 0);
          CHECK(beyond - beyond == 0);
  
          ++it;
          CHECK(it - first == 1);
          CHECK(*it == 2);
          *it = 22;
          CHECK(*it == 22);
          CHECK(beyond - it == 3);
  
          it = first;
          CHECK(it == first);
          while (it != s.end()) {
              *it = 5;
              ++it;
          }
  
          CHECK(it == beyond);
          CHECK(it - beyond == 0);
  
          for (const auto& n : s) {
              CHECK(n == 5);
          }
      }
  }
  
  GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
  TEST_CASE("cbegin_cend")
  {
      {
          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);
          CHECK(cit == cit2);
  
          cit = s.cend();
          cit2 = std::cend(s);
          CHECK(cit == cit2);
      }
  
      {
          int a[] = {1, 2, 3, 4};
          span<int> s = a;
  
          auto it = s.cbegin();
          auto first = it;
          CHECK(it == first);
          CHECK(*it == 1);
  
          auto beyond = s.cend();
          CHECK(it != beyond);
          CHECK_THROWS_AS(*beyond, fail_fast);
  
          CHECK(beyond - first == 4);
          CHECK(first - first == 0);
          CHECK(beyond - beyond == 0);
  
          ++it;
          CHECK(it - first == 1);
          CHECK(*it == 2);
          CHECK(beyond - it == 3);
  
          int last = 0;
          it = first;
          CHECK(it == first);
          while (it != s.cend()) {
              CHECK(*it == last + 1);
  
              last = *it;
              ++it;
          }
  
          CHECK(it == beyond);
          CHECK(it - beyond == 0);
      }
  }
  
  GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
  TEST_CASE("rbegin_rend")
  {
      {
          int a[] = {1, 2, 3, 4};
          span<int> s = a;
  
          auto it = s.rbegin();
          auto first = it;
          CHECK(it == first);
          CHECK(*it == 4);
  
          auto beyond = s.rend();
          CHECK(it != beyond);
          CHECK_THROWS_AS(*beyond, fail_fast);
  
          CHECK(beyond - first == 4);
          CHECK(first - first == 0);
          CHECK(beyond - beyond == 0);
  
          ++it;
          CHECK(it - first == 1);
          CHECK(*it == 3);
          *it = 22;
          CHECK(*it == 22);
          CHECK(beyond - it == 3);
  
          it = first;
          CHECK(it == first);
          while (it != s.rend()) {
              *it = 5;
              ++it;
          }
  
          CHECK(it == beyond);
          CHECK(it - beyond == 0);
  
          for (const auto& n : s) {
              CHECK(n == 5);
          }
      }
  }
  
  GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
  TEST_CASE("crbegin_crend")
  {
      {
          int a[] = {1, 2, 3, 4};
          span<int> s = a;
  
          auto it = s.crbegin();
          auto first = it;
          CHECK(it == first);
          CHECK(*it == 4);
  
          auto beyond = s.crend();
          CHECK(it != beyond);
          CHECK_THROWS_AS(*beyond, fail_fast);
  
          CHECK(beyond - first == 4);
          CHECK(first - first == 0);
          CHECK(beyond - beyond == 0);
  
          ++it;
          CHECK(it - first == 1);
          CHECK(*it == 3);
          CHECK(beyond - it == 3);
  
          it = first;
          CHECK(it == first);
          int last = 5;
          while (it != s.crend()) {
              CHECK(*it == last - 1);
              last = *it;
  
              ++it;
          }
  
          CHECK(it == beyond);
          CHECK(it - beyond == 0);
      }
  }
  
  GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
  TEST_CASE("comparison_operators")
  {
      {
          span<int> s1;
          span<int> s2;
          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};
          span<int> s1 = arr;
          span<int> s2 = arr;
  
          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;
          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));
      }
  }
  
  GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
  TEST_CASE("as_bytes")
  {
      int a[] = {1, 2, 3, 4};
  
      {
          const span<const int> s = a;
          CHECK(s.size() == 4);
          const span<const byte> bs = as_bytes(s);
          CHECK(static_cast<const void*>(bs.data()) == static_cast<const void*>(s.data()));
          CHECK(bs.size() == s.size_bytes());
      }
  
      {
          span<int> s;
          const auto bs = as_bytes(s);
          CHECK(bs.size() == s.size());
          CHECK(bs.size() == 0);
          CHECK(bs.size_bytes() == 0);
          CHECK(static_cast<const void*>(bs.data()) == static_cast<const void*>(s.data()));
          CHECK(bs.data() == nullptr);
      }
  
      {
          span<int> s = a;
          const auto bs = as_bytes(s);
          CHECK(static_cast<const void*>(bs.data()) == static_cast<const void*>(s.data()));
          CHECK(bs.size() == s.size_bytes());
      }
  }
  
  GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
  TEST_CASE("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> s = a;
          CHECK(s.size() == 4);
          span<const byte> bs = as_writeable_bytes(s);
          CHECK(static_cast<void*>(bs.data()) == static_cast<void*>(s.data()));
          CHECK(bs.size() == s.size_bytes());
  #endif
      }
  
      {
          span<int> s;
          const auto bs = as_writeable_bytes(s);
          CHECK(bs.size() == s.size());
          CHECK(bs.size() == 0);
          CHECK(bs.size_bytes() == 0);
          CHECK(static_cast<void*>(bs.data()) == static_cast<void*>(s.data()));
          CHECK(bs.data() == nullptr);
      }
  
      {
          span<int> s = a;
          const auto bs = as_writeable_bytes(s);
          CHECK(static_cast<void*>(bs.data()) == static_cast<void*>(s.data()));
          CHECK(bs.size() == s.size_bytes());
      }
  }
  
  GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
  TEST_CASE("fixed_size_conversions")
  {
      int arr[] = {1, 2, 3, 4};
  
      // converting to an span from an equal size array is ok
      span<int, 4> s4 = arr;
      CHECK(s4.size() == 4);
  
      // converting to dynamic_range is always ok
      {
          span<int> s = s4;
          CHECK(s.size() == s4.size());
          static_cast<void>(s);
      }
  
  // initialization or assignment to static span that REDUCES size is NOT ok
  #ifdef CONFIRM_COMPILATION_ERRORS
      {
          span<int, 2> s = arr;
      }
      {
          span<int, 2> s2 = s4;
          static_cast<void>(s2);
      }
  #endif
  
      // even when done dynamically
      {
          span<int> s = arr;
          auto f = [&]() {
              const span<int, 2> s2 = s;
              static_cast<void>(s2);
          };
          CHECK_THROWS_AS(f(), fail_fast);
      }
  
      // but doing so explicitly is ok
  
      // you can convert statically
      {
          const span<int, 2> s2 = {&arr[0], 2};
          static_cast<void>(s2);
      }
      {
          const span<int, 1> s1 = s4.first<1>();
          static_cast<void>(s1);
      }
  
      // ...or dynamically
      {
          // NB: implicit conversion to span<int,1> from span<int>
          span<int, 1> s1 = s4.first(1);
          static_cast<void>(s1);
      }
  
      // initialization or assignment to static span that requires size INCREASE is not ok.
      int arr2[2] = {1, 2};
  
  #ifdef CONFIRM_COMPILATION_ERRORS
      {
          span<int, 4> s3 = arr2;
      }
      {
          span<int, 2> s2 = arr2;
          span<int, 4> s4a = s2;
      }
  #endif
      {
          auto f = [&]() {
              const span<int, 4> _s4 = {arr2, 2};
              static_cast<void>(_s4);
          };
          CHECK_THROWS_AS(f(), fail_fast);
      }
  
      // this should fail - we are trying to assign a small dynamic span to a fixed_size larger one
      span<int> av = arr2;
      auto f = [&]() {
          const span<int, 4> _s4 = av;
          static_cast<void>(_s4);
      };
      CHECK_THROWS_AS(f(), fail_fast);
  }
  
  GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
  TEST_CASE("interop_with_std_regex")
  {
      char lat[] = {'1', '2', '3', '4', '5', '6', 'E', 'F', 'G'};
      span<char> s = lat;
      const auto f_it = s.begin() + 7;
  
      std::match_results<span<char>::iterator> match;
  
      std::regex_match(s.begin(), s.end(), match, std::regex(".*"));
      CHECK(match.ready());
      CHECK(!match.empty());
      CHECK(match[0].matched);
      CHECK(match[0].first == s.begin());
      CHECK(match[0].second == s.end());
  
      std::regex_search(s.begin(), s.end(), match, std::regex("F"));
      CHECK(match.ready());
      CHECK(!match.empty());
      CHECK(match[0].matched);
      CHECK(match[0].first == f_it);
      CHECK(match[0].second == (f_it + 1));
  }
  
  GSL_SUPPRESS(con.4) // NO-FORMAT: attribute
  TEST_CASE("interop_with_gsl_at")
  {
      int arr[5] = {1, 2, 3, 4, 5};
      span<int> s{arr};
      CHECK((at(s, 0) == 1 && at(s, 1) == 2));
  }
  
  TEST_CASE("default_constructible")
  {
      CHECK((std::is_default_constructible<span<int>>::value));
      CHECK((std::is_default_constructible<span<int, 0>>::value));
      CHECK((!std::is_default_constructible<span<int, 42>>::value));
  }
  
  