libcxx/test/std/strings/basic.string/string.nonmembers/string.special/swap_noexcept.pass.cpp

   1 //===----------------------------------------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 // UNSUPPORTED: c++03
  10
  11 // <string>
  12
  13 // void swap(basic_string& c)
  14 //     noexcept(!allocator_type::propagate_on_container_swap::value ||
  15 //              __is_nothrow_swappable<allocator_type>::value); // constexpr since C++20
  16 //
  17 //  In C++17, the standard says that swap shall have:
  18 //     noexcept(allocator_traits<Allocator>::propagate_on_container_swap::value ||
  19 //              allocator_traits<Allocator>::is_always_equal::value); // constexpr since C++20
  20
  21 // This tests a conforming extension
  22
  23 #include <string>
  24 #include <utility>
  25 #include <cassert>
  26
  27 #include "test_macros.h"
  28 #include "test_allocator.h"
  29
  30 template <class T>
  31 struct some_alloc {
  32   typedef T value_type;
  33
  34   some_alloc() {}
  35   some_alloc(const some_alloc&);
  36   T* allocate(std::size_t);
  37   void deallocate(void*, unsigned) {}
  38   typedef std::true_type propagate_on_container_swap;
  39 };
  40
  41 template <class T>
  42 struct some_alloc2 {
  43   typedef T value_type;
  44
  45   some_alloc2() {}
  46   some_alloc2(const some_alloc2&);
  47   T* allocate(std::size_t);
  48   void deallocate(void*, unsigned) {}
  49
  50   typedef std::false_type propagate_on_container_swap;
  51   typedef std::true_type is_always_equal;
  52 };
  53
  54 int main(int, char**) {
  55   {
  56     typedef std::string C;
  57     static_assert(noexcept(swap(std::declval<C&>(), std::declval<C&>())), "");
  58   }
  59 #if defined(_LIBCPP_VERSION)
  60   {
  61     typedef std::basic_string<char, std::char_traits<char>, test_allocator<char>> C;
  62     static_assert(noexcept(swap(std::declval<C&>(), std::declval<C&>())), "");
  63   }
  64 #endif // _LIBCPP_VERSION
  65   {
  66     typedef std::basic_string<char, std::char_traits<char>, some_alloc<char>> C;
  67 #if TEST_STD_VER >= 14
  68     //  In C++14, if POCS is set, swapping the allocator is required not to throw
  69     static_assert(noexcept(swap(std::declval<C&>(), std::declval<C&>())), "");
  70 #else
  71     static_assert(!noexcept(swap(std::declval<C&>(), std::declval<C&>())), "");
  72 #endif
  73   }
  74 #if TEST_STD_VER >= 14
  75   {
  76     typedef std::basic_string<char, std::char_traits<char>, some_alloc2<char>> C;
  77     //  if the allocators are always equal, then the swap can be noexcept
  78     static_assert(noexcept(swap(std::declval<C&>(), std::declval<C&>())), "");
  79   }
  80 #endif
  81
  82   return 0;
  83 }