2 * Copyright 2017 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.
19 // included by Future.h, do not include directly.
23 template <class> class Promise;
26 struct isFuture : std::false_type {
27 using Inner = typename Unit::Lift<T>::type;
31 struct isFuture<Future<T>> : std::true_type {
36 struct isTry : std::false_type {};
39 struct isTry<Try<T>> : std::true_type {};
44 template <class> class Core;
45 template <class...> struct CollectAllVariadicContext;
46 template <class...> struct CollectVariadicContext;
47 template <class> struct CollectContext;
49 template<typename F, typename... Args>
50 using resultOf = decltype(std::declval<F>()(std::declval<Args>()...));
52 template <typename...>
55 template <typename Arg, typename... Args>
56 struct ArgType<Arg, Args...> {
62 typedef void FirstArg;
65 template <bool isTry, typename F, typename... Args>
67 using Result = resultOf<F, Args...>;
70 template<typename F, typename... Args>
73 typename = detail::resultOf<T, Args...>>
74 static constexpr std::true_type
75 check(std::nullptr_t) { return std::true_type{}; }
78 static constexpr std::false_type
79 check(...) { return std::false_type{}; }
81 typedef decltype(check<F>(nullptr)) type;
82 static constexpr bool value = type::value;
85 template<typename T, typename F>
86 struct callableResult {
87 typedef typename std::conditional<
88 callableWith<F>::value,
89 detail::argResult<false, F>,
90 typename std::conditional<
91 callableWith<F, T&&>::value,
92 detail::argResult<false, F, T&&>,
93 typename std::conditional<
94 callableWith<F, T&>::value,
95 detail::argResult<false, F, T&>,
96 typename std::conditional<
97 callableWith<F, Try<T>&&>::value,
98 detail::argResult<true, F, Try<T>&&>,
99 detail::argResult<true, F, Try<T>&>>::type>::type>::type>::type Arg;
100 typedef isFuture<typename Arg::Result> ReturnsFuture;
101 typedef Future<typename ReturnsFuture::Inner> Return;
104 template <typename L>
105 struct Extract : Extract<decltype(&L::operator())> { };
107 template <typename Class, typename R, typename... Args>
108 struct Extract<R(Class::*)(Args...) const> {
109 typedef isFuture<R> ReturnsFuture;
110 typedef Future<typename ReturnsFuture::Inner> Return;
111 typedef typename ReturnsFuture::Inner RawReturn;
112 typedef typename ArgType<Args...>::FirstArg FirstArg;
115 template <typename Class, typename R, typename... Args>
116 struct Extract<R(Class::*)(Args...)> {
117 typedef isFuture<R> ReturnsFuture;
118 typedef Future<typename ReturnsFuture::Inner> Return;
119 typedef typename ReturnsFuture::Inner RawReturn;
120 typedef typename ArgType<Args...>::FirstArg FirstArg;
123 template <typename R, typename... Args>
124 struct Extract<R (*)(Args...)> {
125 typedef isFuture<R> ReturnsFuture;
126 typedef Future<typename ReturnsFuture::Inner> Return;
127 typedef typename ReturnsFuture::Inner RawReturn;
128 typedef typename ArgType<Args...>::FirstArg FirstArg;
131 template <typename R, typename... Args>
132 struct Extract<R (&)(Args...)> {
133 typedef isFuture<R> ReturnsFuture;
134 typedef Future<typename ReturnsFuture::Inner> Return;
135 typedef typename ReturnsFuture::Inner RawReturn;
136 typedef typename ArgType<Args...>::FirstArg FirstArg;
139 } // namespace detail
140 } // namespace futures