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, c++11, c++14
10
11// <variant>
12
13// template <class ...Types> class variant;
14
15// template <size_t I, class ...Args>
16// variant_alternative_t<I, variant<Types...>>& emplace(Args&&... args);
17
18#include <cassert>
19#include <string>
20#include <type_traits>
21#include <variant>
22
23#include "archetypes.h"
24#include "test_convertible.h"
25#include "test_macros.h"
26#include "variant_test_helpers.h"
27
28template <class Var, std::size_t I, class... Args>
29constexpr auto test_emplace_exists_imp(int)
30 -> decltype(std::declval<Var>().template emplace<I>(std::declval<Args>()...), true) {
31 return true;
32}
33
34template <class, std::size_t, class...>
35constexpr auto test_emplace_exists_imp(long) -> bool {
36 return false;
37}
38
39template <class Var, std::size_t I, class... Args>
40constexpr bool emplace_exists() {
41 return test_emplace_exists_imp<Var, I, Args...>(0);
42}
43
44constexpr void test_emplace_sfinae() {
45 {
46 using V = std::variant<int, void*, const void*, TestTypes::NoCtors>;
47 static_assert(emplace_exists<V, 0>(), "");
48 static_assert(emplace_exists<V, 0, int>(), "");
49 static_assert(!emplace_exists<V, 0, decltype(nullptr)>(), "cannot construct");
50 static_assert(emplace_exists<V, 1, decltype(nullptr)>(), "");
51 static_assert(emplace_exists<V, 1, int*>(), "");
52 static_assert(!emplace_exists<V, 1, const int*>(), "");
53 static_assert(!emplace_exists<V, 1, int>(), "cannot construct");
54 static_assert(emplace_exists<V, 2, const int*>(), "");
55 static_assert(emplace_exists<V, 2, int*>(), "");
56 static_assert(!emplace_exists<V, 3>(), "cannot construct");
57 }
58}
59
60struct NoCtor {
61 NoCtor() = delete;
62};
63
64TEST_CONSTEXPR_CXX20 void test_basic() {
65 {
66 using V = std::variant<int>;
67 V v(42);
68 auto& ref1 = v.emplace<0>();
69 static_assert(std::is_same_v<int&, decltype(ref1)>, "");
70 assert(std::get<0>(v) == 0);
71 assert(&ref1 == &std::get<0>(v));
72 auto& ref2 = v.emplace<0>(args: 42);
73 static_assert(std::is_same_v<int&, decltype(ref2)>, "");
74 assert(std::get<0>(v) == 42);
75 assert(&ref2 == &std::get<0>(v));
76 }
77
78 {
79 using V = std::variant<int, long, const void*, NoCtor, std::string>;
80 const int x = 100;
81 V v(std::in_place_index<0>, -1);
82 // default emplace a value
83 auto& ref1 = v.emplace<1>();
84 static_assert(std::is_same_v<long&, decltype(ref1)>, "");
85 assert(std::get<1>(v) == 0);
86 assert(&ref1 == &std::get<1>(v));
87 auto& ref2 = v.emplace<2>(args: &x);
88 static_assert(std::is_same_v<const void*&, decltype(ref2)>, "");
89 assert(std::get<2>(v) == &x);
90 assert(&ref2 == &std::get<2>(v));
91 // emplace with multiple args
92 auto& ref3 = v.emplace<4>(args: 3u, args: 'a');
93 static_assert(std::is_same_v<std::string&, decltype(ref3)>, "");
94 assert(std::get<4>(v) == "aaa");
95 assert(&ref3 == &std::get<4>(v));
96 }
97}
98
99TEST_CONSTEXPR_CXX20 bool test() {
100 test_basic();
101 test_emplace_sfinae();
102
103 return true;
104}
105
106int main(int, char**) {
107 test();
108
109#if TEST_STD_VER >= 20
110 static_assert(test());
111#endif
112
113 return 0;
114}
115

source code of libcxx/test/std/utilities/variant/variant.variant/variant.mod/emplace_index_args.pass.cpp