зеркало из https://github.com/mozilla/gecko-dev.git
111 строки
2.9 KiB
C++
111 строки
2.9 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim: set ts=8 sts=2 et sw=2 tw=80: */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this file,
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* You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef mozilla_dom_Nullable_h
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#define mozilla_dom_Nullable_h
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#include <ostream>
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#include <utility>
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#include "mozilla/Assertions.h"
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#include "mozilla/Maybe.h"
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#include "nsTArrayForwardDeclare.h"
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class nsCycleCollectionTraversalCallback;
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namespace mozilla {
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namespace dom {
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// Support for nullable types
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template <typename T>
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struct Nullable {
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private:
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Maybe<T> mValue;
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public:
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Nullable() : mValue() {}
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MOZ_IMPLICIT Nullable(const decltype(nullptr)&) : mValue() {}
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explicit Nullable(const T& aValue) : mValue() { mValue.emplace(aValue); }
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MOZ_IMPLICIT Nullable(T&& aValue) : mValue() {
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mValue.emplace(std::move(aValue));
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}
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Nullable(Nullable<T>&& aOther) : mValue(std::move(aOther.mValue)) {}
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Nullable(const Nullable<T>& aOther) : mValue(aOther.mValue) {}
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void operator=(const Nullable<T>& aOther) { mValue = aOther.mValue; }
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void SetValue(const T& aArgs) {
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mValue.reset();
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mValue.emplace(aArgs);
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}
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void SetValue(T&& aArgs) {
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mValue.reset();
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mValue.emplace(std::move(aArgs));
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}
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// For cases when |T| is some type with nontrivial copy behavior, we may want
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// to get a reference to our internal copy of T and work with it directly
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// instead of relying on the copying version of SetValue().
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T& SetValue() {
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if (mValue.isNothing()) {
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mValue.emplace();
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}
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return mValue.ref();
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}
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void SetNull() { mValue.reset(); }
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const T& Value() const { return mValue.ref(); }
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T& Value() { return mValue.ref(); }
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bool IsNull() const { return mValue.isNothing(); }
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bool Equals(const Nullable<T>& aOtherNullable) const {
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return mValue == aOtherNullable.mValue;
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}
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bool operator==(const Nullable<T>& aOtherNullable) const {
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return Equals(aOtherNullable);
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}
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bool operator!=(const Nullable<T>& aOtherNullable) const {
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return !Equals(aOtherNullable);
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}
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friend std::ostream& operator<<(std::ostream& aStream,
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const Nullable& aNullable) {
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return aStream << aNullable.mValue;
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}
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};
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template <typename T>
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void ImplCycleCollectionTraverse(nsCycleCollectionTraversalCallback& aCallback,
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Nullable<T>& aNullable, const char* aName,
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uint32_t aFlags = 0) {
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if (!aNullable.IsNull()) {
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ImplCycleCollectionTraverse(aCallback, aNullable.Value(), aName, aFlags);
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}
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}
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template <typename T>
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void ImplCycleCollectionUnlink(Nullable<T>& aNullable) {
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if (!aNullable.IsNull()) {
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ImplCycleCollectionUnlink(aNullable.Value());
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}
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}
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} // namespace dom
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} // namespace mozilla
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#endif /* mozilla_dom_Nullable_h */
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