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

//===----------------------------------------------------------------------===//
//
// 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++03

// <string>

// void swap(basic_string& c)
//     noexcept(!allocator_type::propagate_on_container_swap::value ||
//              __is_nothrow_swappable<allocator_type>::value); // constexpr since C++20
//
//  In C++17, the standard says that swap shall have:
//     noexcept(allocator_traits<Allocator>::propagate_on_container_swap::value ||
//              allocator_traits<Allocator>::is_always_equal::value); // constexpr since C++20

// This tests a conforming extension

#include <string>
#include <utility>
#include <cassert>

#include "test_macros.h"
#include "test_allocator.h"

template <class T>
struct some_alloc {
  typedef T value_type;

  some_alloc() {}
  some_alloc(const some_alloc&);
  T* allocate(std::size_t);
  void deallocate(void*, unsigned) {}
  typedef std::true_type propagate_on_container_swap;
};

template <class T>
struct some_alloc2 {
  typedef T value_type;

  some_alloc2() {}
  some_alloc2(const some_alloc2&);
  T* allocate(std::size_t);
  void deallocate(void*, unsigned) {}

  typedef std::false_type propagate_on_container_swap;
  typedef std::true_type is_always_equal;
};

int main(int, char**) {
  {
    typedef std::string C;
    static_assert(noexcept(swap(std::declval<C&>(), std::declval<C&>())), "");
  }
#if defined(_LIBCPP_VERSION)
  {
    typedef std::basic_string<char, std::char_traits<char>, test_allocator<char>> C;
    static_assert(noexcept(swap(std::declval<C&>(), std::declval<C&>())), "");
  }
#endif // _LIBCPP_VERSION
  {
    typedef std::basic_string<char, std::char_traits<char>, some_alloc<char>> C;
#if TEST_STD_VER >= 14
    //  In C++14, if POCS is set, swapping the allocator is required not to throw
    static_assert(noexcept(swap(std::declval<C&>(), std::declval<C&>())), "");
#else
    static_assert(!noexcept(swap(std::declval<C&>(), std::declval<C&>())), "");
#endif
  }
#if TEST_STD_VER >= 14
  {
    typedef std::basic_string<char, std::char_traits<char>, some_alloc2<char>> C;
    //  if the allocators are always equal, then the swap can be noexcept
    static_assert(noexcept(swap(std::declval<C&>(), std::declval<C&>())), "");
  }
#endif

  return 0;
}