Add mozilla::AutoRestore to restore values at the end of a C++ scope. (Bug 518756) r=bsmedberg

xpcom/glue/AutoRestore.h

@@ -0,0 +1,70 @@
+/* vim: set shiftwidth=2 tabstop=8 autoindent cindent expandtab: */
+/* ***** BEGIN LICENSE BLOCK *****
+ * Version: MPL 1.1/GPL 2.0/LGPL 2.1
+ *
+ * The contents of this file are subject to the Mozilla Public License Version
+ * 1.1 (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ * http://www.mozilla.org/MPL/
+ *
+ * Software distributed under the License is distributed on an "AS IS" basis,
+ * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
+ * for the specific language governing rights and limitations under the
+ * License.
+ *
+ * The Original Code is nsAutoRestore.h.
+ *
+ * The Initial Developer of the Original Code is the Mozilla Foundation.
+ * Portions created by the Initial Developer are Copyright (C) 2009
+ * the Initial Developer. All Rights Reserved.
+ *
+ * Contributor(s):
+ *   L. David Baron <dbaron@dbaron.org>, Mozilla Corporation (original author)
+ *
+ * Alternatively, the contents of this file may be used under the terms of
+ * either the GNU General Public License Version 2 or later (the "GPL"), or
+ * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
+ * in which case the provisions of the GPL or the LGPL are applicable instead
+ * of those above. If you wish to allow use of your version of this file only
+ * under the terms of either the GPL or the LGPL, and not to allow others to
+ * use your version of this file under the terms of the MPL, indicate your
+ * decision by deleting the provisions above and replace them with the notice
+ * and other provisions required by the GPL or the LGPL. If you do not delete
+ * the provisions above, a recipient may use your version of this file under
+ * the terms of any one of the MPL, the GPL or the LGPL.
+ *
+ * ***** END LICENSE BLOCK ***** */
+
+/* functions for restoring saved values at the end of a C++ scope */
+
+#ifndef mozilla_AutoRestore_h_
+#define mozilla_AutoRestore_h_
+
+namespace mozilla {
+
+  /**
+   * Save the current value of a variable and restore it when the object
+   * goes out of scope.  For example:
+   *   {
+   *     AutoRestore<PRBool> savePainting(mIsPainting);
+   *     mIsPainting = PR_TRUE;
+   *     
+   *     // ... your code here ...
+   *
+   *     // mIsPainting is reset to its old value at the end of this block
+   *   }
+   */
+  template <class T>
+  class AutoRestore
+  {
+  private:
+    T& mLocation;
+    T mValue;
+  public:
+    AutoRestore(T& aValue) : mLocation(aValue), mValue(aValue) {}
+    ~AutoRestore() { mLocation = mValue; }
+  };
+
+}
+
+#endif /* !defined(mozilla_AutoRestore_h_) */

xpcom/glue/Makefile.in

@@ -124,6 +124,7 @@ EXPORTS = \
 		$(NULL)
 
 EXPORTS_mozilla = \
+  AutoRestore.h \
   BlockingResourceBase.h \
   CondVar.h \
   DeadlockDetector.h \