79 lines
2.4 KiB
C
79 lines
2.4 KiB
C
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/*
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* Copyright (c) Facebook, Inc. and its affiliates.
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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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#pragma once
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#include <array>
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#include <type_traits>
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#include <utility>
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#include <folly/CPortability.h>
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#include <folly/Traits.h>
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#include <folly/Utility.h>
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namespace folly {
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namespace array_detail {
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template <class T>
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using is_ref_wrapper = detail::is_instantiation_of<std::reference_wrapper, T>;
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template <typename T>
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using not_ref_wrapper =
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folly::Negation<is_ref_wrapper<typename std::decay<T>::type>>;
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template <typename D, typename...>
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struct return_type_helper {
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using type = D;
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};
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template <typename... TList>
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struct return_type_helper<void, TList...> {
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static_assert(
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folly::Conjunction<not_ref_wrapper<TList>...>::value,
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"TList cannot contain reference_wrappers when D is void");
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using type = typename std::common_type<TList...>::type;
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};
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template <typename D, typename... TList>
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using return_type = std::
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array<typename return_type_helper<D, TList...>::type, sizeof...(TList)>;
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} // namespace array_detail
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template <typename D = void, typename... TList>
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constexpr array_detail::return_type<D, TList...> make_array(TList&&... t) {
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using value_type =
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typename array_detail::return_type_helper<D, TList...>::type;
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return {{static_cast<value_type>(std::forward<TList>(t))...}};
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}
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namespace array_detail {
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template <typename MakeItem, std::size_t... Index>
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FOLLY_ERASE constexpr auto make_array_with_(
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MakeItem const& make,
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std::index_sequence<Index...>) {
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return std::array<decltype(make(0)), sizeof...(Index)>{{make(Index)...}};
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}
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} // namespace array_detail
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// make_array_with
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//
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// Constructs a std::array<..., Size> with elements m(i) for i in [0, Size).
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template <std::size_t Size, typename MakeItem>
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constexpr auto make_array_with(MakeItem const& make) {
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return array_detail::make_array_with_(make, std::make_index_sequence<Size>{});
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}
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} // namespace folly
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