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+/*
+ * Copyright (c) 2003-2007, John Wiegley.  All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ * - Redistributions of source code must retain the above copyright
+ *   notice, this list of conditions and the following disclaimer.
+ *
+ * - Redistributions in binary form must reproduce the above copyright
+ *   notice, this list of conditions and the following disclaimer in the
+ *   documentation and/or other materials provided with the distribution.
+ *
+ * - Neither the name of New Artisans LLC nor the names of its
+ *   contributors may be used to endorse or promote products derived from
+ *   this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+/**
+ * @file   pushvar.h
+ * @author John Wiegley
+ * @date   Sun May  6 20:10:52 2007
+ *
+ * @brief  Adds a facility to C++ for handling "scoped yet global".
+ */
+
+#ifndef _PUSHVAR_H
+#define _PUSHVAR_H
+
+template <typename T>
+class push_variable : public boost::noncopyable
+{
+  push_variable();
+
+public:
+  T&   var;
+  T    prev;
+  bool enabled;
+
+  explicit push_variable(T& _var)
+    : var(_var), prev(var), enabled(true) {
+    TRACE_CTOR(push_variable, "T&");
+  }
+  explicit push_variable(T& _var, const T& value)
+    : var(_var), prev(var), enabled(true) {
+    TRACE_CTOR(push_variable, "T&, constT&");
+    var = value;
+  }
+  ~push_variable() throw() {
+    TRACE_DTOR(push_variable);
+    if (enabled)
+      var = prev;
+  }
+
+  T& operator*() {
+    return var;
+  }
+  T * operator->() {
+    return &var;
+  }
+
+  void clear() {
+    enabled = false;
+  }
+};
+
+#endif // _PUSHVAR_H