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