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125 lines
3.9 KiB
C++
125 lines
3.9 KiB
C++
/*
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* Copyright 2016 Facebook, Inc.
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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/*
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* Defines a function folly::applyTuple, which takes a function and a
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* std::tuple of arguments and calls the function with those
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* arguments.
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*
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* Example:
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*
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* int x = folly::applyTuple(std::plus<int>(), std::make_tuple(12, 12));
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* ASSERT(x == 24);
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*/
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#pragma once
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#include <functional>
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#include <tuple>
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#include <utility>
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namespace folly {
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//////////////////////////////////////////////////////////////////////
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namespace detail {
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namespace apply_tuple {
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template <std::size_t...>
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struct IndexSequence {};
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template <std::size_t N, std::size_t... Is>
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struct MakeIndexSequence : MakeIndexSequence<N - 1, N - 1, Is...> {};
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template <std::size_t... Is>
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struct MakeIndexSequence<0, Is...> : IndexSequence<Is...> {};
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inline constexpr std::size_t sum() {
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return 0;
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}
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template <typename... Args>
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inline constexpr std::size_t sum(std::size_t v1, Args... vs) {
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return v1 + sum(vs...);
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}
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template <typename... Tuples>
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struct TupleSizeSum {
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static constexpr auto value = sum(std::tuple_size<Tuples>::value...);
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};
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template <typename... Tuples>
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using MakeIndexSequenceFromTuple = MakeIndexSequence<
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TupleSizeSum<typename std::decay<Tuples>::type...>::value>;
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// This is to allow using this with pointers to member functions,
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// where the first argument in the tuple will be the this pointer.
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template <class F>
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inline constexpr F&& makeCallable(F&& f) {
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return std::forward<F>(f);
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}
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template <class M, class C>
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inline constexpr auto makeCallable(M(C::*d)) -> decltype(std::mem_fn(d)) {
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return std::mem_fn(d);
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}
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template <class F, class Tuple, std::size_t... Indexes>
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inline constexpr auto call(F&& f, Tuple&& t, IndexSequence<Indexes...>)
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-> decltype(
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std::forward<F>(f)(std::get<Indexes>(std::forward<Tuple>(t))...)) {
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return std::forward<F>(f)(std::get<Indexes>(std::forward<Tuple>(t))...);
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}
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template <class Tuple, std::size_t... Indexes>
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inline constexpr auto forwardTuple(Tuple&& t, IndexSequence<Indexes...>)
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-> decltype(
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std::forward_as_tuple(std::get<Indexes>(std::forward<Tuple>(t))...)) {
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return std::forward_as_tuple(std::get<Indexes>(std::forward<Tuple>(t))...);
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}
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} // namespace apply_tuple
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} // namespace detail
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//////////////////////////////////////////////////////////////////////
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/**
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* Invoke a callable object with a set of arguments passed as a tuple, or a
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* series of tuples
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*
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* Example: the following lines are equivalent
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* func(1, 2, 3, "foo");
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* applyTuple(func, std::make_tuple(1, 2, 3, "foo"));
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* applyTuple(func, std::make_tuple(1, 2), std::make_tuple(3, "foo"));
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*/
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template <class F, class... Tuples>
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inline constexpr auto applyTuple(F&& f, Tuples&&... t)
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-> decltype(detail::apply_tuple::call(
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detail::apply_tuple::makeCallable(std::forward<F>(f)),
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std::tuple_cat(detail::apply_tuple::forwardTuple(
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std::forward<Tuples>(t),
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detail::apply_tuple::MakeIndexSequenceFromTuple<Tuples>{})...),
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detail::apply_tuple::MakeIndexSequenceFromTuple<Tuples...>{})) {
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return detail::apply_tuple::call(
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detail::apply_tuple::makeCallable(std::forward<F>(f)),
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std::tuple_cat(detail::apply_tuple::forwardTuple(
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std::forward<Tuples>(t),
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detail::apply_tuple::MakeIndexSequenceFromTuple<Tuples>{})...),
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detail::apply_tuple::MakeIndexSequenceFromTuple<Tuples...>{});
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}
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//////////////////////////////////////////////////////////////////////
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}
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