77 lines
2.1 KiB
C++
77 lines
2.1 KiB
C++
/*
|
|
* Copyright (c) Facebook, Inc. and its affiliates.
|
|
*
|
|
* Licensed under the Apache License, Version 2.0 (the "License");
|
|
* you may not use this file except in compliance with the License.
|
|
* You may obtain a copy of the License at
|
|
*
|
|
* http://www.apache.org/licenses/LICENSE-2.0
|
|
*
|
|
* Unless required by applicable law or agreed to in writing, software
|
|
* distributed under the License is distributed on an "AS IS" BASIS,
|
|
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
|
|
* See the License for the specific language governing permissions and
|
|
* limitations under the License.
|
|
*/
|
|
|
|
#pragma once
|
|
|
|
#include <type_traits>
|
|
|
|
namespace folly {
|
|
namespace fibers {
|
|
|
|
/**
|
|
* For any functor F taking >= 1 argument,
|
|
* FirstArgOf<F>::type is the type of F's first parameter.
|
|
*
|
|
* Rationale: we want to declare a function func(F), where F has the
|
|
* signature `void(X)` and func should return T<X> (T and X are some types).
|
|
* Solution:
|
|
*
|
|
* template <typename F>
|
|
* T<typename FirstArgOf<F>::type>
|
|
* func(F&& f);
|
|
*/
|
|
|
|
namespace detail {
|
|
|
|
template <typename F>
|
|
struct ExtractFirstArg;
|
|
|
|
template <typename Ret, typename T, typename First, typename... Args>
|
|
struct ExtractFirstArg<Ret (T::*)(First, Args...)> {
|
|
typedef First type;
|
|
};
|
|
|
|
template <typename Ret, typename T, typename First, typename... Args>
|
|
struct ExtractFirstArg<Ret (T::*)(First, Args...) const> {
|
|
typedef First type;
|
|
};
|
|
|
|
template <typename Ret, typename First, typename... Args>
|
|
struct ExtractFirstArg<Ret(First, Args...)> {
|
|
typedef First type;
|
|
};
|
|
|
|
} // namespace detail
|
|
|
|
template <typename F, typename Enable = void>
|
|
struct FirstArgOf;
|
|
|
|
/** Specialization for non-function-object callables */
|
|
template <typename F>
|
|
struct FirstArgOf<F, typename std::enable_if<!std::is_class<F>::value>::type> {
|
|
typedef typename detail::ExtractFirstArg<
|
|
typename std::remove_pointer<F>::type>::type type;
|
|
};
|
|
|
|
/** Specialization for function objects */
|
|
template <typename F>
|
|
struct FirstArgOf<F, typename std::enable_if<std::is_class<F>::value>::type> {
|
|
typedef typename FirstArgOf<decltype(&F::operator())>::type type;
|
|
};
|
|
|
|
} // namespace fibers
|
|
} // namespace folly
|