103 lines
2.9 KiB
C++
103 lines
2.9 KiB
C++
/*
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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 <initializer_list>
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#include <iterator>
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#include <folly/Portability.h>
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#include <folly/functional/Invoke.h>
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namespace folly {
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namespace access {
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// mimic: std::size, C++17
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struct size_fn {
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template <typename C>
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FOLLY_ERASE constexpr auto operator()(C const& c) const
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noexcept(noexcept(c.size())) -> decltype(c.size()) {
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return c.size();
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}
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template <typename T, std::size_t N>
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FOLLY_ERASE constexpr std::size_t operator()(T const (&)[N]) const noexcept {
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return N;
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}
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};
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FOLLY_INLINE_VARIABLE constexpr size_fn size{};
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// mimic: std::empty, C++17
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struct empty_fn {
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template <typename C>
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FOLLY_ERASE constexpr auto operator()(C const& c) const
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noexcept(noexcept(c.empty())) -> decltype(c.empty()) {
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return c.empty();
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}
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template <typename T, std::size_t N>
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FOLLY_ERASE constexpr bool operator()(T const (&)[N]) const noexcept {
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// while zero-length arrays are not allowed in the language, some compilers
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// may permit them in some cases
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return N == 0;
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}
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template <typename E>
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FOLLY_ERASE constexpr bool operator()(
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std::initializer_list<E> il) const noexcept {
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return il.size() == 0;
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}
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};
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FOLLY_INLINE_VARIABLE constexpr empty_fn empty{};
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// mimic: std::data, C++17
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struct data_fn {
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template <typename C>
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FOLLY_ERASE constexpr auto operator()(C& c) const noexcept(noexcept(c.data()))
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-> decltype(c.data()) {
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return c.data();
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}
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template <typename C>
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FOLLY_ERASE constexpr auto operator()(C const& c) const
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noexcept(noexcept(c.data())) -> decltype(c.data()) {
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return c.data();
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}
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template <typename T, std::size_t N>
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FOLLY_ERASE constexpr T* operator()(T (&a)[N]) const noexcept {
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return a;
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}
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template <typename E>
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FOLLY_ERASE constexpr E const* operator()(
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std::initializer_list<E> il) const noexcept {
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return il.begin();
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}
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};
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FOLLY_INLINE_VARIABLE constexpr data_fn data{};
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// begin
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//
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// Invokes unqualified begin with std::begin in scope.
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FOLLY_CREATE_FREE_INVOKER(begin_fn, begin, std);
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FOLLY_INLINE_VARIABLE constexpr begin_fn begin{};
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// end
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//
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// Invokes unqualified end with std::end in scope.
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FOLLY_CREATE_FREE_INVOKER(end_fn, end, std);
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FOLLY_INLINE_VARIABLE constexpr end_fn end{};
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} // namespace access
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} // namespace folly
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