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47 行
1.5 KiB
47 行
1.5 KiB
// Copyright (c) 2018 The LevelDB Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file. See the AUTHORS file for names of contributors.
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#ifndef STORAGE_LEVELDB_UTIL_NO_DESTRUCTOR_H_
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#define STORAGE_LEVELDB_UTIL_NO_DESTRUCTOR_H_
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#include <type_traits>
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#include <utility>
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namespace leveldb {
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// Wraps an instance whose destructor is never called.
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//
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// This is intended for use with function-level static variables.
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template<typename InstanceType>
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class NoDestructor {
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public:
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template <typename... ConstructorArgTypes>
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explicit NoDestructor(ConstructorArgTypes&&... constructor_args) {
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static_assert(sizeof(instance_storage_) >= sizeof(InstanceType),
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"instance_storage_ is not large enough to hold the instance");
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static_assert(
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alignof(decltype(instance_storage_)) >= alignof(InstanceType),
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"instance_storage_ does not meet the instance's alignment requirement");
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new (&instance_storage_) InstanceType(
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std::forward<ConstructorArgTypes>(constructor_args)...);
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}
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~NoDestructor() = default;
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NoDestructor(const NoDestructor&) = delete;
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NoDestructor& operator=(const NoDestructor&) = delete;
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InstanceType* get() {
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return reinterpret_cast<InstanceType*>(&instance_storage_);
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}
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private:
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typename
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std::aligned_storage<sizeof(InstanceType), alignof(InstanceType)>::type
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instance_storage_;
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};
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} // namespace leveldb
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#endif // STORAGE_LEVELDB_UTIL_NO_DESTRUCTOR_H_
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