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1 | // Copyright (c) 2011-present, Facebook, Inc. All rights reserved. |
2 | // This source code is licensed under both the GPLv2 (found in the | |
3 | // COPYING file in the root directory) and Apache 2.0 License | |
4 | // (found in the LICENSE.Apache file in the root directory). | |
5 | ||
6 | #pragma once | |
7 | ||
8 | #include <folly/Traits.h> | |
9 | ||
10 | #include <functional> | |
11 | #include <type_traits> | |
12 | ||
13 | namespace folly { | |
14 | namespace invoke_detail { | |
15 | template <typename F, typename... Args> | |
16 | using invoke_result_ = decltype(std::declval<F>()(std::declval<Args>()...)); | |
17 | ||
18 | template <typename Void, typename F, typename... Args> | |
19 | struct is_invocable : std::false_type {}; | |
20 | ||
21 | template <typename F, typename... Args> | |
22 | struct is_invocable<void_t<invoke_result_<F, Args...>>, F, Args...> | |
23 | : std::true_type {}; | |
24 | ||
25 | template <typename Void, typename R, typename F, typename... Args> | |
26 | struct is_invocable_r : std::false_type {}; | |
27 | ||
28 | template <typename R, typename F, typename... Args> | |
29 | struct is_invocable_r<void_t<invoke_result_<F, Args...>>, R, F, Args...> | |
30 | : std::is_convertible<invoke_result_<F, Args...>, R> {}; | |
31 | } // namespace invoke_detail | |
32 | ||
33 | // mimic: std::is_invocable, C++17 | |
34 | template <typename F, typename... Args> | |
35 | struct is_invocable : invoke_detail::is_invocable<void, F, Args...> {}; | |
36 | ||
37 | // mimic: std::is_invocable_r, C++17 | |
38 | template <typename R, typename F, typename... Args> | |
39 | struct is_invocable_r : invoke_detail::is_invocable_r<void, R, F, Args...> {}; | |
40 | } // namespace folly |