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// <utility>
10
11// template <class T1, class T2> struct pair
12// void swap(const pair& p) const;
13
14// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
15
16#include <cassert>
17#include <utility>
18
19#include "test_macros.h"
20
21// Remarks: The expression inside noexcept is equivalent to
22// is_nothrow_swappable_v<const first_type> && is_nothrow_swappable_v<const second_type> for the second overload.
23template <class T>
24concept ConstMemberSwapNoexcept =
25 requires(const T& t1, const T& t2) {
26 { t1.swap(t2) } noexcept;
27 };
28
29template <bool canThrow>
30struct SwapMayThrow {};
31
32template <bool canThrow>
33void swap(const SwapMayThrow<canThrow>&, const SwapMayThrow<canThrow>&) noexcept(!canThrow);
34
35static_assert(ConstMemberSwapNoexcept<std::pair<SwapMayThrow<false>, SwapMayThrow<false>>>);
36static_assert(!ConstMemberSwapNoexcept<std::pair<SwapMayThrow<true>, SwapMayThrow<false>>>);
37static_assert(!ConstMemberSwapNoexcept<std::pair<SwapMayThrow<false>, SwapMayThrow<true>>>);
38static_assert(!ConstMemberSwapNoexcept<std::pair<SwapMayThrow<true>, SwapMayThrow<true>>>);
39
40struct ConstSwappable {
41 mutable int i;
42 friend constexpr void swap(const ConstSwappable& lhs, const ConstSwappable& rhs) { std::swap(a&: lhs.i, b&: rhs.i); }
43};
44
45constexpr bool test() {
46 // user defined const swap
47 {
48 using P = std::pair<const ConstSwappable, const ConstSwappable>;
49 const P p1(ConstSwappable{.i: 0}, ConstSwappable{.i: 1});
50 const P p2(ConstSwappable{.i: 2}, ConstSwappable{.i: 3});
51 p1.swap(p2);
52 assert(p1.first.i == 2);
53 assert(p1.second.i == 3);
54 assert(p2.first.i == 0);
55 assert(p2.second.i == 1);
56 }
57
58 // pair of references
59 {
60 int i1 = 0, i2 = 1, i3 = 2, i4 = 3;
61 const std::pair<int&, int&> p1{i1, i2};
62 const std::pair<int&, int&> p2{i3, i4};
63 p1.swap(p2);
64 assert(p1.first == 2);
65 assert(p1.second == 3);
66 assert(p2.first == 0);
67 assert(p2.second == 1);
68 }
69 return true;
70}
71
72int main(int, char**) {
73 test();
74
75// gcc cannot have mutable member in constant expression
76#if !defined(TEST_COMPILER_GCC)
77 static_assert(test());
78#endif
79
80 return 0;
81}

source code of libcxx/test/std/utilities/utility/pairs/pairs.pair/swap_member_const.pass.cpp