tor-browser

The Tor Browser
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nsAttrValueOrString.h (2772B)

      1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
      2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
      3 /* This Source Code Form is subject to the terms of the Mozilla Public
      4 * License, v. 2.0. If a copy of the MPL was not distributed with this file,
      5 * You can obtain one at http://mozilla.org/MPL/2.0/. */
      6 
      7 /*
      8 * A wrapper to contain either an nsAttrValue or an nsAString. This is useful
      9 * because constructing an nsAttrValue from an nsAString can be expensive when
     10 * the buffer of the string is not shared.
     11 *
     12 * This treats nsAttrValueOrString(nullptr) as the empty string,
     13 * to help with contexts where a null pointer denotes an empty value.
     14 *
     15 * Since a raw pointer to the passed-in string is kept, this class should only
     16 * be used on the stack.
     17 */
     18 
     19 #ifndef nsAttrValueOrString_h___
     20 #define nsAttrValueOrString_h___
     21 
     22 #include "nsAttrValue.h"
     23 #include "nsString.h"
     24 
     25 class MOZ_STACK_CLASS nsAttrValueOrString {
     26 public:
     27  explicit nsAttrValueOrString(const nsAString& aValue)
     28      : mAttrValue(nullptr), mStringPtr(&aValue), mCheapString(nullptr) {}
     29 
     30  explicit nsAttrValueOrString(const nsAString* aValue)
     31      : mAttrValue(nullptr), mStringPtr(aValue), mCheapString(nullptr) {}
     32 
     33  explicit nsAttrValueOrString(const nsAttrValue& aValue)
     34      : mAttrValue(&aValue), mStringPtr(nullptr), mCheapString(nullptr) {}
     35 
     36  explicit nsAttrValueOrString(const nsAttrValue* aValue)
     37      : mAttrValue(aValue), mStringPtr(nullptr), mCheapString(nullptr) {}
     38 
     39  void ResetToAttrValue(const nsAttrValue& aValue) {
     40    mAttrValue = &aValue;
     41    mStringPtr = nullptr;
     42    // No need to touch mCheapString here.  If we need to use it, we will reset
     43    // it to the rigthe value anyway.
     44  }
     45 
     46  /**
     47   * Returns a reference to the string value of the contents of this object.
     48   *
     49   * When this object points to a string or an nsAttrValue of string or atom
     50   * type this should be fairly cheap. Other nsAttrValue types will be
     51   * serialized the first time this is called and cached from thereon.
     52   */
     53  const nsAString& String() const;
     54 
     55  /**
     56   * Compares the string representation of this object with the string
     57   * representation of an nsAttrValue.
     58   */
     59  bool EqualsAsStrings(const nsAttrValue& aOther) const {
     60    if (mStringPtr) {
     61      return aOther.Equals(*mStringPtr, eCaseMatters);
     62    }
     63    return aOther.EqualsAsStrings(*mAttrValue);
     64  }
     65 
     66  /*
     67   * Returns true if the value stored is empty
     68   */
     69  bool IsEmpty() const {
     70    if (mStringPtr) {
     71      return mStringPtr->IsEmpty();
     72    }
     73    if (mAttrValue) {
     74      return mAttrValue->IsEmptyString();
     75    }
     76    return true;
     77  }
     78 
     79 protected:
     80  const nsAttrValue* mAttrValue;
     81  mutable const nsAString* mStringPtr;
     82  mutable nsCheapString mCheapString;
     83 };
     84 
     85 #endif  // nsAttrValueOrString_h___