text: //===----------------------------------------------------------------------===//
  //
  // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
  // See https://llvm.org/LICENSE.txt for license information.
  // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
  //
  //===----------------------------------------------------------------------===//
  // UNSUPPORTED: c++98, c++03, c++11, c++14, c++17
  
  // <span>
  
  // constexpr       iterator  end() const noexcept;
  // constexpr const_iterator cend() const noexcept;
  
  #include <span>
  #include <cassert>
  #include <string>
  
  #include "test_macros.h"
  
  template <class Span>
  constexpr bool testConstexprSpan(Span s)
  {
      bool ret = true;
      typename Span::iterator e        = s. end();
      typename Span::const_iterator ce = s.cend();
      if (s.empty())
      {
          ret = ret &&  ( e ==  s.begin());
          ret = ret &&  (ce == s.cbegin());
      }
      else
      {
      	typename Span::const_pointer last = &*(s.cbegin() + s.size() - 1);
          ret = ret &&  ( e !=  s.begin());
          ret = ret &&  (ce != s.cbegin());
          ret = ret &&  (&*( e-1) == last);
          ret = ret &&  (&*(ce-1) == last);
      }
  
      ret = ret &&  (static_cast<size_t>( e -  s.begin()) == s.size());
      ret = ret &&  (static_cast<size_t>(ce - s.cbegin()) == s.size());
  
      ret = ret &&  (e == ce);
      return ret;
  }
  
  template <class Span>
  void testRuntimeSpan(Span s)
  {
      typename Span::iterator e        = s. end();
      typename Span::const_iterator ce = s.cend();
      if (s.empty())
      {
          assert( e ==  s.begin());
          assert(ce == s.cbegin());
      }
      else
      {
      	typename Span::const_pointer last = &*(s.cbegin() + s.size() - 1);
          assert( e !=  s.begin());
          assert(ce != s.cbegin());
          assert( &*( e-1) == last);
          assert( &*(ce-1) == last);
      }
  
      assert(static_cast<size_t>( e -  s.begin()) == s.size());
      assert(static_cast<size_t>(ce - s.cbegin()) == s.size());
  
      assert(e == ce);
  }
  
  
  struct A{};
  bool operator==(A, A) {return true;}
  
  constexpr int iArr1[] = { 0,  1,  2,  3,  4,  5,  6,  7,  8,  9};
            int iArr2[] = {10, 11, 12, 13, 14, 15, 16, 17, 18, 19};
  
  
  int main(int, char**)
  {
      static_assert(testConstexprSpan(std::span<int>()),            "");
      static_assert(testConstexprSpan(std::span<long>()),           "");
      static_assert(testConstexprSpan(std::span<double>()),         "");
      static_assert(testConstexprSpan(std::span<A>()),              "");
      static_assert(testConstexprSpan(std::span<std::string>()),    "");
  
      static_assert(testConstexprSpan(std::span<int, 0>()),         "");
      static_assert(testConstexprSpan(std::span<long, 0>()),        "");
      static_assert(testConstexprSpan(std::span<double, 0>()),      "");
      static_assert(testConstexprSpan(std::span<A, 0>()),           "");
      static_assert(testConstexprSpan(std::span<std::string, 0>()), "");
  
      static_assert(testConstexprSpan(std::span<const int>(iArr1, 1)),    "");
      static_assert(testConstexprSpan(std::span<const int>(iArr1, 2)),    "");
      static_assert(testConstexprSpan(std::span<const int>(iArr1, 3)),    "");
      static_assert(testConstexprSpan(std::span<const int>(iArr1, 4)),    "");
      static_assert(testConstexprSpan(std::span<const int>(iArr1, 5)),    "");
  
  
      testRuntimeSpan(std::span<int>        ());
      testRuntimeSpan(std::span<long>       ());
      testRuntimeSpan(std::span<double>     ());
      testRuntimeSpan(std::span<A>          ());
      testRuntimeSpan(std::span<std::string>());
  
      testRuntimeSpan(std::span<int, 0>        ());
      testRuntimeSpan(std::span<long, 0>       ());
      testRuntimeSpan(std::span<double, 0>     ());
      testRuntimeSpan(std::span<A, 0>          ());
      testRuntimeSpan(std::span<std::string, 0>());
  
      testRuntimeSpan(std::span<int>(iArr2, 1));
      testRuntimeSpan(std::span<int>(iArr2, 2));
      testRuntimeSpan(std::span<int>(iArr2, 3));
      testRuntimeSpan(std::span<int>(iArr2, 4));
      testRuntimeSpan(std::span<int>(iArr2, 5));
  
      std::string s;
      testRuntimeSpan(std::span<std::string>(&s, (std::size_t) 0));
      testRuntimeSpan(std::span<std::string>(&s, 1));
  
    return 0;
  }
  