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, c++17, c++20
10 // <optional>
11 
12 // template<class F> constexpr optional or_else(F&&) &&;
13 // template<class F> constexpr optional or_else(F&&) const&;
14 
15 #include "MoveOnly.h"
16 
17 #include <cassert>
18 #include <optional>
19 
20 struct NonMovable {
21   NonMovable() = default;
22   NonMovable(NonMovable&&) = delete;
23 };
24 
25 template <class Opt, class F>
26 concept has_or_else = requires(Opt&& opt, F&& f) {
27   {std::forward<Opt>(opt).or_else(std::forward<F>(f))};
28 };
29 
30 template <class T>
31 std::optional<T> return_optional() {}
32 
33 static_assert(has_or_else<std::optional<int>&, decltype(return_optional<int>)>);
34 static_assert(has_or_else<std::optional<int>&&, decltype(return_optional<int>)>);
35 static_assert(!has_or_else<std::optional<MoveOnly>&, decltype(return_optional<MoveOnly>)>);
36 static_assert(has_or_else<std::optional<MoveOnly>&&, decltype(return_optional<MoveOnly>)>);
37 static_assert(!has_or_else<std::optional<NonMovable>&, decltype(return_optional<NonMovable>)>);
38 static_assert(!has_or_else<std::optional<NonMovable>&&, decltype(return_optional<NonMovable>)>);
39 
40 std::optional<int> take_int(int) { return 0; }
41 void take_int_return_void(int) {}
42 
43 static_assert(!has_or_else<std::optional<int>, decltype(take_int)>);
44 static_assert(!has_or_else<std::optional<int>, decltype(take_int_return_void)>);
45 static_assert(!has_or_else<std::optional<int>, int>);
46 
47 constexpr bool test() {
48   {
49     std::optional<int> opt;
50     assert(opt.or_else([] { return std::optional<int>{0}; }) == 0);
51     opt = 1;
52     opt.or_else([] {
53       assert(false);
54       return std::optional<int>{};
55     });
56   }
57   {
58     std::optional<MoveOnly> opt;
59     opt = std::move(opt).or_else([] { return std::optional<MoveOnly>{MoveOnly{}}; });
60     std::move(opt).or_else([] {
61       assert(false);
62       return std::optional<MoveOnly>{};
63     });
64   }
65 
66   return true;
67 }
68 
69 int main(int, char**) {
70   test();
71   static_assert(test());
72   return 0;
73 }
74