chromium/third_party/angle/src/common/base/anglebase/no_destructor.h

// Copyright 2018 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef ANGLEBASE_NO_DESTRUCTOR_H_
#define ANGLEBASE_NO_DESTRUCTOR_H_

#include <new>
#include <utility>

namespace angle
{

namespace base
{

// A wrapper that makes it easy to create an object of type T with static
// storage duration that:
// - is only constructed on first access
// - never invokes the destructor
// in order to satisfy the styleguide ban on global constructors and
// destructors.
//
// Runtime constant example:
// const std::string& GetLineSeparator() {
//  // Forwards to std::string(size_t, char, const Allocator&) constructor.
//   static const base::NoDestructor<std::string> s(5, '-');
//   return *s;
// }
//
// More complex initialization with a lambda:
// const std::string& GetSessionNonce() {
//   static const base::NoDestructor<std::string> nonce([] {
//     std::string s(16);
//     crypto::RandString(s.data(), s.size());
//     return s;
//   }());
//   return *nonce;
// }
//
// NoDestructor<T> stores the object inline, so it also avoids a pointer
// indirection and a malloc. Also note that since C++11 static local variable
// initialization is thread-safe and so is this pattern. Code should prefer to
// use NoDestructor<T> over:
// - A function scoped static T* or T& that is dynamically initialized.
// - A global base::LazyInstance<T>.
//
// Note that since the destructor is never run, this *will* leak memory if used
// as a stack or member variable. Furthermore, a NoDestructor<T> should never
// have global scope as that may require a static initializer.
template <typename T>
class NoDestructor
{ … };

}  // namespace base

}  // namespace angle

#endif  // ANGLEBASE_NO_DESTRUCTOR_H_