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
28 template <class Var, std::size_t I, class... Args>
test_emplace_exists_imp(int)29 constexpr auto test_emplace_exists_imp(int)
30 -> decltype(std::declval<Var>().template emplace<I>(std::declval<Args>()...), true) {
31 return true;
32 }
33
34 template <class, std::size_t, class...>
test_emplace_exists_imp(long)35 constexpr auto test_emplace_exists_imp(long) -> bool {
36 return false;
37 }
38
39 template <class Var, std::size_t I, class... Args>
emplace_exists()40 constexpr bool emplace_exists() {
41 return test_emplace_exists_imp<Var, I, Args...>(0);
42 }
43
test_emplace_sfinae()44 constexpr 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
60 struct NoCtor {
61 NoCtor() = delete;
62 };
63
test_basic()64 TEST_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>(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>(&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>(3u, '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
test()99 TEST_CONSTEXPR_CXX20 bool test() {
100 test_basic();
101 test_emplace_sfinae();
102
103 return true;
104 }
105
main(int,char **)106 int main(int, char**) {
107 test();
108
109 #if TEST_STD_VER >= 20
110 static_assert(test());
111 #endif
112
113 return 0;
114 }
115