new file, a small idea

git-svn-id: svn://localhost/ardour2/branches/3.0@11257 d708f5d6-7413-0410-9779-e7cbd77b26cf

libs/pbd/pbd/unwind.h

@@ -0,0 +1,38 @@
+/*
+    Copyright (C) 2012 Paul Davis 
+
+    This program is free software; you can redistribute it and/or modify
+    it under the terms of the GNU General Public License as published by
+    the Free Software Foundation; either version 2 of the License, or
+    (at your option) any later version.
+
+    This program is distributed in the hope that it will be useful,
+    but WITHOUT ANY WARRANTY; without even the implied warranty of
+    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+    GNU General Public License for more details.
+
+    You should have received a copy of the GNU General Public License
+    along with this program; if not, write to the Free Software
+    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+
+*/
+
+#ifndef __libpbd_unwinder_h__
+#define __libpbd_unwinder_h__
+
+namespace PBD {
+
+template <typename T>
+class Unwinder {
+  public:
+    Unwinder (T& var, T new_val) : _var (var), _old_val (var) { var = new_val; }
+    ~Unwinder () { _var = _old_val; }
+		
+  private:
+    T& _var;
+    T  _old_val;
+};
+
+}
+
+#endif /* __libpbd_unwinder_h__ */