third_party/llvm-project/libcxx/test/std/utilities/utility/pairs/pairs.pair/swap_member_const.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
//
//===----------------------------------------------------------------------===//

// <utility>

// template <class T1, class T2> struct pair
// void swap(const pair& p) const;

// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20

#include <cassert>
#include <utility>

#include "test_macros.h"

// Remarks: The expression inside noexcept is equivalent to
// is_nothrow_swappable_v<const first_type> && is_nothrow_swappable_v<const second_type> for the second overload.
template <class T>
concept ConstMemberSwapNoexcept =
    requires(const T& t1, const T& t2) {
      { t1.swap(t2) } noexcept;
    };

template <bool canThrow>
struct SwapMayThrow {};

template <bool canThrow>
void swap(const SwapMayThrow<canThrow>&, const SwapMayThrow<canThrow>&) noexcept(!canThrow);

static_assert(ConstMemberSwapNoexcept<std::pair<SwapMayThrow<false>, SwapMayThrow<false>>>);
static_assert(!ConstMemberSwapNoexcept<std::pair<SwapMayThrow<true>, SwapMayThrow<false>>>);
static_assert(!ConstMemberSwapNoexcept<std::pair<SwapMayThrow<false>, SwapMayThrow<true>>>);
static_assert(!ConstMemberSwapNoexcept<std::pair<SwapMayThrow<true>, SwapMayThrow<true>>>);

struct ConstSwappable {
  mutable int i;
  friend constexpr void swap(const ConstSwappable& lhs, const ConstSwappable& rhs) { std::swap(lhs.i, rhs.i); }
};

constexpr bool test() {
  // user defined const swap
  {
    using P = std::pair<const ConstSwappable, const ConstSwappable>;
    const P p1(ConstSwappable{0}, ConstSwappable{1});
    const P p2(ConstSwappable{2}, ConstSwappable{3});
    p1.swap(p2);
    assert(p1.first.i == 2);
    assert(p1.second.i == 3);
    assert(p2.first.i == 0);
    assert(p2.second.i == 1);
  }

  // pair of references
  {
    int i1 = 0, i2 = 1, i3 = 2, i4 = 3;
    const std::pair<int&, int&> p1{i1, i2};
    const std::pair<int&, int&> p2{i3, i4};
    p1.swap(p2);
    assert(p1.first == 2);
    assert(p1.second == 3);
    assert(p2.first == 0);
    assert(p2.second == 1);
  }
  return true;
}

int main(int, char**) {
  test();

// gcc cannot have mutable member in constant expression
#if !defined(TEST_COMPILER_GCC)
  static_assert(test());
#endif

  return 0;
}