// Copyright (c) 2011 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 BASE_AUTO_RESET_H_ #define BASE_AUTO_RESET_H_ #include #include "base/memory/raw_ptr_exclusion.h" // base::AutoReset<> is useful for setting a variable to a new value only within // a particular scope. An base::AutoReset<> object resets a variable to its // original value upon destruction, making it an alternative to writing // "var = false;" or "var = old_val;" at all of a block's exit points. // // This should be obvious, but note that an base::AutoReset<> instance should // have a shorter lifetime than its scoped_variable, to prevent invalid memory // writes when the base::AutoReset<> object is destroyed. namespace base { template class AutoReset { public: template AutoReset(T* scoped_variable, U&& new_value) : scoped_variable_(scoped_variable), original_value_( std::exchange(*scoped_variable_, std::forward(new_value))) {} AutoReset(AutoReset&& other) : scoped_variable_(std::exchange(other.scoped_variable_, nullptr)), original_value_(std::move(other.original_value_)) {} AutoReset& operator=(AutoReset&& rhs) { scoped_variable_ = std::exchange(rhs.scoped_variable_, nullptr); original_value_ = std::move(rhs.original_value_); return *this; } ~AutoReset() { if (scoped_variable_) *scoped_variable_ = std::move(original_value_); } private: // `scoped_variable_` is not a raw_ptr for performance reasons: Large // number of non-PartitionAlloc pointees + AutoReset is typically short-lived // (e.g. allocated on the stack). RAW_PTR_EXCLUSION T* scoped_variable_; T original_value_; }; } // namespace base #endif // BASE_AUTO_RESET_H_