82 lines
2.8 KiB
C++
82 lines
2.8 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 <folly/Portability.h>
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#include <folly/functional/Invoke.h>
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#include <folly/lang/CustomizationPoint.h>
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namespace folly {
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// order_preserving_reinsertion_view_fn
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// order_preserving_reinsertion_view
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//
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// Extension point for containers to provide an order such that if entries are
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// inserted into a new instance in that order, iteration order of the new
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// instance matches the original's. This can be useful for containers that have
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// defined but non-FIFO iteration order, such as F14Vector*.
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//
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// Should return an iterable view (a type that provides begin() and end()).
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//
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// Containers should provide overloads via tag-invoke.
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struct order_preserving_reinsertion_view_fn {
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private:
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using fn = order_preserving_reinsertion_view_fn;
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public:
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template <typename Container>
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FOLLY_ERASE constexpr auto operator()(Container const& container) const
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noexcept(is_nothrow_tag_invocable_v<fn, Container const&>)
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-> tag_invoke_result_t<fn, Container const&> {
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return tag_invoke(*this, container);
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}
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};
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FOLLY_DEFINE_CPO(
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order_preserving_reinsertion_view_fn, order_preserving_reinsertion_view)
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// order_preserving_reinsertion_view_or_default_fn
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// order_preserving_reinsertion_view_or_default
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//
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// If a tag-invoke extension of order_preserving_reinsertion_view is available
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// over the given argument, forwards to that. Otherwise, returns the argument.
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struct order_preserving_reinsertion_view_or_default_fn {
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private:
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using fn = order_preserving_reinsertion_view_fn;
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public:
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template <
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typename Container,
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std::enable_if_t<is_tag_invocable_v<fn, Container const&>, int> = 0>
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FOLLY_ERASE constexpr auto operator()(Container const& container) const
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noexcept(is_nothrow_tag_invocable_v<fn, Container const&>)
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-> tag_invoke_result_t<fn, Container const&> {
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return tag_invoke(fn{}, container);
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}
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template <
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typename Container,
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std::enable_if_t<!is_tag_invocable_v<fn, Container const&>, int> = 0>
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FOLLY_ERASE constexpr Container const& operator()(
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Container const& container) const noexcept {
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return container;
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}
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};
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FOLLY_DEFINE_CPO(
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order_preserving_reinsertion_view_or_default_fn,
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order_preserving_reinsertion_view_or_default)
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} // namespace folly
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