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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 */
* A wrapper to contain either an nsAttrValue or an nsAString. This is useful
* because constructing an nsAttrValue from an nsAString can be expensive when
* the buffer of the string is not shared.
* This treats nsAttrValueOrString(nullptr) as the empty string,
* to help with contexts where a null pointer denotes an empty value.
* Since a raw pointer to the passed-in string is kept, this class should only
* be used on the stack.
#ifndef nsAttrValueOrString_h___
#define nsAttrValueOrString_h___
#include "nsString.h"
#include "nsAttrValue.h"
class MOZ_STACK_CLASS nsAttrValueOrString {
explicit nsAttrValueOrString(const nsAString& aValue)
: mAttrValue(nullptr), mStringPtr(&aValue), mCheapString(nullptr) {}
explicit nsAttrValueOrString(const nsAString* aValue)
: mAttrValue(nullptr), mStringPtr(aValue), mCheapString(nullptr) {}
explicit nsAttrValueOrString(const nsAttrValue& aValue)
: mAttrValue(&aValue), mStringPtr(nullptr), mCheapString(nullptr) {}
explicit nsAttrValueOrString(const nsAttrValue* aValue)
: mAttrValue(aValue), mStringPtr(nullptr), mCheapString(nullptr) {}
void ResetToAttrValue(const nsAttrValue& aValue) {
mAttrValue = &aValue;
mStringPtr = nullptr;
// No need to touch mCheapString here. If we need to use it, we will reset
// it to the rigthe value anyway.
* Returns a reference to the string value of the contents of this object.
* When this object points to a string or an nsAttrValue of string or atom
* type this should be fairly cheap. Other nsAttrValue types will be
* serialized the first time this is called and cached from thereon.
const nsAString& String() const;
* Compares the string representation of this object with the string
* representation of an nsAttrValue.
bool EqualsAsStrings(const nsAttrValue& aOther) const {
if (mStringPtr) {
return aOther.Equals(*mStringPtr, eCaseMatters);
return aOther.EqualsAsStrings(*mAttrValue);
* Returns true if the value stored is empty
bool IsEmpty() const {
if (mStringPtr) {
return mStringPtr->IsEmpty();
if (mAttrValue) {
return mAttrValue->IsEmptyString();
return true;
const nsAttrValue* mAttrValue;
mutable const nsAString* mStringPtr;
mutable nsCheapString mCheapString;
#endif // nsAttrValueOrString_h___