70 lines
2.3 KiB
C++
70 lines
2.3 KiB
C++
// Copyright 2022 The Chromium Authors
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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.
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#ifndef BASE_MEMORY_VALUES_EQUIVALENT_H_
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#define BASE_MEMORY_VALUES_EQUIVALENT_H_
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#include <functional>
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#include <memory>
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#include "base/memory/scoped_refptr.h"
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namespace base {
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// Compares two pointers for equality, returns the dereferenced value comparison
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// if both are non-null.
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// Behaves like std::optional<T>::operator==(const std::optional<T>&) but for
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// pointers, with an optional predicate.
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// If `p` is specified, `p(const T& x, const T& y)` should return whether `x`
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// and `y` are equal. It's called with `(*a, *b)` when `a != b && a && b`.
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template <typename T, typename Predicate = std::equal_to<>>
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bool ValuesEquivalent(const T* a, const T* b, Predicate p = {}) {
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if (a == b)
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return true;
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if (!a || !b)
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return false;
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return p(*a, *b);
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}
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// Specialize for smart pointers like std::unique_ptr and base::scoped_refptr
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// that provide a T* get() method.
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// Example usage:
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// struct Example {
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// std::unique_ptr<Child> child;
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// bool operator==(const Example& other) const {
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// return base::ValuesEquivalent(child, other.child);
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// }
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// };
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template <typename T,
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typename Predicate = std::equal_to<>,
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std::enable_if_t<
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std::is_pointer_v<decltype(std::declval<T>().get())>>* = nullptr>
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bool ValuesEquivalent(const T& x, const T& y, Predicate p = {}) {
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return ValuesEquivalent(x.get(), y.get(), std::move(p));
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}
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// Specialize for smart pointers like blink::Persistent and blink::Member that
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// provide a T* Get() method.
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// Example usage:
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// namespace blink {
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// struct Example : public GarbageCollected<Example> {
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// Member<Child> child;
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// bool operator==(const Example& other) const {
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// return base::ValuesEquivalent(child, other.child);
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// }
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// void Trace(Visitor*) const;
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// };
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// } // namespace blink
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template <typename T,
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typename Predicate = std::equal_to<>,
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std::enable_if_t<
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std::is_pointer_v<decltype(std::declval<T>().Get())>>* = nullptr>
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bool ValuesEquivalent(const T& x, const T& y, Predicate p = {}) {
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return ValuesEquivalent(x.Get(), y.Get(), std::move(p));
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}
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} // namespace base
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#endif // BASE_MEMORY_VALUES_EQUIVALENT_H_
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