1 // Copyright 2011 The Chromium Authors
2 // Use of this source code is governed by a BSD-style license that can be
3 // found in the LICENSE file.
5 #ifndef BASE_AUTO_RESET_H_
6 #define BASE_AUTO_RESET_H_
10 #include "base/memory/raw_ptr_exclusion.h"
12 // base::AutoReset<> is useful for setting a variable to a new value only within
13 // a particular scope. An base::AutoReset<> object resets a variable to its
14 // original value upon destruction, making it an alternative to writing
15 // "var = false;" or "var = old_val;" at all of a block's exit points.
17 // This should be obvious, but note that an base::AutoReset<> instance should
18 // have a shorter lifetime than its scoped_variable, to prevent invalid memory
19 // writes when the base::AutoReset<> object is destroyed.
27 AutoReset(T* scoped_variable, U&& new_value)
28 : scoped_variable_(scoped_variable),
30 std::exchange(*scoped_variable_, std::forward<U>(new_value))) {}
32 AutoReset(AutoReset&& other)
33 : scoped_variable_(std::exchange(other.scoped_variable_, nullptr)),
34 original_value_(std::move(other.original_value_)) {}
36 AutoReset& operator=(AutoReset&& rhs) {
37 scoped_variable_ = std::exchange(rhs.scoped_variable_, nullptr);
38 original_value_ = std::move(rhs.original_value_);
44 *scoped_variable_ = std::move(original_value_);
48 // `scoped_variable_` is not a raw_ptr<T> for performance reasons: Large
49 // number of non-PartitionAlloc pointees + AutoReset is typically short-lived
50 // (e.g. allocated on the stack).
51 RAW_PTR_EXCLUSION T* scoped_variable_;
58 #endif // BASE_AUTO_RESET_H_