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89 lines
2.1 KiB
C++
89 lines
2.1 KiB
C++
/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-*/
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/* vim: set ts=2 sw=2 et tw=79: */
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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 "mozilla/Assertions.h"
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#include "nsTArrayForwardDeclare.h"
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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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{
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private:
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// mIsNull MUST COME FIRST because otherwise the casting in our array
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// conversion operators would shift where it is found in the struct.
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bool mIsNull;
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T mValue;
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public:
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Nullable()
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: mIsNull(true)
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{}
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explicit Nullable(T aValue)
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: mIsNull(false)
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, mValue(aValue)
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{}
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void SetValue(T aValue) {
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mValue = aValue;
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mIsNull = false;
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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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mIsNull = false;
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return mValue;
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}
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void SetNull() {
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mIsNull = true;
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}
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const T& Value() const {
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MOZ_ASSERT(!mIsNull);
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return mValue;
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}
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T& Value() {
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MOZ_ASSERT(!mIsNull);
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return mValue;
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}
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bool IsNull() const {
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return mIsNull;
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}
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// Make it possible to use a const Nullable of an array type with other
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// array types.
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template<typename U>
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operator const Nullable< nsTArray<U> >&() const {
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// Make sure that T is ok to reinterpret to nsTArray<U>
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const nsTArray<U>& arr = mValue;
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(void)arr;
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return *reinterpret_cast<const Nullable< nsTArray<U> >*>(this);
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}
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template<typename U>
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operator const Nullable< FallibleTArray<U> >&() const {
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// Make sure that T is ok to reinterpret to FallibleTArray<U>
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const FallibleTArray<U>& arr = mValue;
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(void)arr;
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return *reinterpret_cast<const Nullable< FallibleTArray<U> >*>(this);
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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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