2 * Copyright 2017-present Facebook, Inc.
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
20 #include <type_traits>
22 #include <folly/Traits.h>
25 * include or backport:
27 * * std::invoke_result
28 * * std::invoke_result_t
30 * * std::is_invocable_r
31 * * std::is_nothrow_invocable
32 * * std::is_nothrow_invocable_r
35 #if __cpp_lib_invoke >= 201411 || _MSC_VER
39 /* using override */ using std::invoke;
47 // mimic: std::invoke, C++17
48 template <typename F, typename... Args>
49 constexpr auto invoke(F&& f, Args&&... args) noexcept(
50 noexcept(std::forward<F>(f)(std::forward<Args>(args)...)))
51 -> decltype(std::forward<F>(f)(std::forward<Args>(args)...)) {
52 return std::forward<F>(f)(std::forward<Args>(args)...);
54 template <typename M, typename C, typename... Args>
55 constexpr auto invoke(M(C::*d), Args&&... args)
56 -> decltype(std::mem_fn(d)(std::forward<Args>(args)...)) {
57 return std::mem_fn(d)(std::forward<Args>(args)...);
64 #if __cpp_lib_is_invocable >= 201703 || _MSC_VER
68 /* using override */ using std::invoke_result;
69 /* using override */ using std::invoke_result_t;
70 /* using override */ using std::is_invocable;
71 /* using override */ using std::is_invocable_r;
72 /* using override */ using std::is_nothrow_invocable;
73 /* using override */ using std::is_nothrow_invocable_r;
83 template <typename F, typename... Args>
84 using invoke_result_ =
85 decltype(invoke(std::declval<F>(), std::declval<Args>()...));
87 template <typename F, typename... Args>
88 using invoke_nothrow_ = std::integral_constant<
90 noexcept(invoke(std::declval<F>(), std::declval<Args>()...))>;
92 // from: http://en.cppreference.com/w/cpp/types/result_of, CC-BY-SA
94 template <typename Void, typename F, typename... Args>
95 struct invoke_result {};
97 template <typename F, typename... Args>
98 struct invoke_result<void_t<invoke_result_<F, Args...>>, F, Args...> {
99 using type = invoke_result_<F, Args...>;
102 template <typename Void, typename F, typename... Args>
103 struct is_invocable : std::false_type {};
105 template <typename F, typename... Args>
106 struct is_invocable<void_t<invoke_result_<F, Args...>>, F, Args...>
109 template <typename Void, typename R, typename F, typename... Args>
110 struct is_invocable_r : std::false_type {};
112 template <typename R, typename F, typename... Args>
113 struct is_invocable_r<void_t<invoke_result_<F, Args...>>, R, F, Args...>
114 : std::is_convertible<invoke_result_<F, Args...>, R> {};
116 template <typename Void, typename F, typename... Args>
117 struct is_nothrow_invocable : std::false_type {};
119 template <typename F, typename... Args>
120 struct is_nothrow_invocable<void_t<invoke_result_<F, Args...>>, F, Args...>
121 : invoke_nothrow_<F, Args...> {};
123 template <typename Void, typename R, typename F, typename... Args>
124 struct is_nothrow_invocable_r : std::false_type {};
126 template <typename R, typename F, typename... Args>
127 struct is_nothrow_invocable_r<void_t<invoke_result_<F, Args...>>, R, F, Args...>
129 std::is_convertible<invoke_result_<F, Args...>, R>,
130 invoke_nothrow_<F, Args...>> {};
132 } // namespace detail
134 // mimic: std::invoke_result, C++17
135 template <typename F, typename... Args>
136 struct invoke_result : detail::invoke_result<void, F, Args...> {};
138 // mimic: std::invoke_result_t, C++17
139 template <typename F, typename... Args>
140 using invoke_result_t = typename invoke_result<F, Args...>::type;
142 // mimic: std::is_invocable, C++17
143 template <typename F, typename... Args>
144 struct is_invocable : detail::is_invocable<void, F, Args...> {};
146 // mimic: std::is_invocable_r, C++17
147 template <typename R, typename F, typename... Args>
148 struct is_invocable_r : detail::is_invocable_r<void, R, F, Args...> {};
150 // mimic: std::is_nothrow_invocable, C++17
151 template <typename F, typename... Args>
152 struct is_nothrow_invocable : detail::is_nothrow_invocable<void, F, Args...> {};
154 // mimic: std::is_nothrow_invocable_r, C++17
155 template <typename R, typename F, typename... Args>
156 struct is_nothrow_invocable_r
157 : detail::is_nothrow_invocable_r<void, R, F, Args...> {};