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