52 lines
1.8 KiB
C
52 lines
1.8 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 <memory>
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#include <type_traits>
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#include <folly/Portability.h>
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#include <folly/Traits.h>
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#include <folly/lang/SafeAssert.h>
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namespace folly {
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// down_cast
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//
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// Unchecked polymorphic down-cast using static_cast. Only works for pairs of
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// types where the cvref-unqualified source type is polymorphic and a base of
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// the target type. The target type, which is passed as an explicit template
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// param, must be cvref-unqualified. The return type is the target type with
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// the same cvref-qualifiers or cvptr-qualifiers as the source type.
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//
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// Checked with an assertion in debug builds.
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template <typename T, typename S>
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FOLLY_ERASE like_t<S, T>* down_cast(S* ptr) noexcept {
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using Q = std::remove_cv_t<S>;
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static_assert(std::is_polymorphic<Q>::value, "not polymorphic");
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static_assert(std::is_base_of<Q, T>::value, "not down-castable");
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using R = like_t<S, T>;
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FOLLY_SAFE_DCHECK(dynamic_cast<R*>(ptr), "not a runtime down-cast");
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return static_cast<R*>(ptr);
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}
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template <typename T, typename S>
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FOLLY_ERASE like_t<S&&, T> down_cast(S&& ref) noexcept {
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return static_cast<like_t<S&&, T>>(*down_cast<T>(std::addressof(ref)));
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}
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} // namespace folly
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