1 files changed, 95 insertions, 0 deletions
diff --git a/dom/base/nsAttrValueOrString.h b/dom/base/nsAttrValueOrString.h
new file mode 100644
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+++ b/dom/base/nsAttrValueOrString.h
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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/. */
+
+/*
+ * 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
+{
+public:
+  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 TakeParsedValue(nsAttrValue& aValue)
+  {
+    mStoredAttrValue.SwapValueWith(aValue);
+    mAttrValue = &mStoredAttrValue;
+    mStringPtr = nullptr;
+  }
+  /**
+   * If TakeParsedValue has been called, returns the value that it set.
+   */
+  nsAttrValue* GetStoredAttrValue()
+  {
+    return mAttrValue == &mStoredAttrValue ? &mStoredAttrValue : nullptr;
+  }
+  const nsAttrValue* GetAttrValue() { return mAttrValue; }
+
+  /**
+   * 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);
+  }
+
+protected:
+  const nsAttrValue*       mAttrValue;
+  mutable const nsAString* mStringPtr;
+  mutable nsCheapString    mCheapString;
+  nsAttrValue              mStoredAttrValue;
+};
+
+#endif // nsAttrValueOrString_h___