87 lines
2.4 KiB
C++
87 lines
2.4 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 <memory>
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namespace folly {
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/** C++11 closures don't support move-in capture. Nor does std::bind.
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facepalm.
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http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2013/n3610.html
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"[...] a work-around that should make people's stomach crawl:
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write a wrapper that performs move-on-copy, much like the deprecated
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auto_ptr"
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Unlike auto_ptr, this doesn't require a heap allocation.
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*/
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template <class T>
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class MoveWrapper {
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public:
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/** If value can be default-constructed, why not?
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Then we don't have to move it in */
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MoveWrapper() = default;
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/// Move a value in.
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explicit MoveWrapper(T&& t) : value(std::move(t)) {}
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/// copy is move
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MoveWrapper(const MoveWrapper& other) : value(std::move(other.value)) {}
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/// move is also move
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MoveWrapper(MoveWrapper&& other) : value(std::move(other.value)) {}
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const T& operator*() const {
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return value;
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}
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T& operator*() {
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return value;
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}
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const T* operator->() const {
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return &value;
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}
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T* operator->() {
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return &value;
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}
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/// move the value out (sugar for std::move(*moveWrapper))
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T&& move() {
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return std::move(value);
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}
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// If you want these you're probably doing it wrong, though they'd be
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// easy enough to implement
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MoveWrapper& operator=(MoveWrapper const&) = delete;
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MoveWrapper& operator=(MoveWrapper&&) = delete;
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private:
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mutable T value;
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};
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/// Make a MoveWrapper from the argument. Because the name "makeMoveWrapper"
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/// is already quite transparent in its intent, this will work for lvalues as
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/// if you had wrapped them in std::move.
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template <class T, class T0 = typename std::remove_reference<T>::type>
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MoveWrapper<T0> makeMoveWrapper(T&& t) {
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return MoveWrapper<T0>(std::forward<T0>(t));
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}
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} // namespace folly
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