scoped: add scoped value restoring class

CMakeLists.txt

@@ -359,6 +359,7 @@ list (
     roots/bisection.hpp
     sarray.cpp
     sarray.hpp
+    scoped.hpp
     si.cpp
     signal.cpp
     signal.hpp

scoped.hpp

@@ -0,0 +1,46 @@
+/*
+ * Licensed under the Apache License, Version 2.0 (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.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ * Copyright 2018, Danny Robson <danny@nerdcruft.net>
+ */
+
+#pragma once
+
+
+namespace util::scoped {
+    ///////////////////////////////////////////////////////////////////////////
+    /// restores a referenced target variable to its original value at
+    /// destruction time. the type must be copyable.
+    template <typename ValueT>
+    class restore {
+    public:
+        restore (ValueT &_target):
+            m_target (_target),
+            m_value  (_target)
+        { ; }
+
+        ~restore ()
+        {
+            m_target = m_value;
+        }
+
+    private:
+        ValueT &m_target;
+        ValueT const m_value;
+    };
+
+
+    //-------------------------------------------------------------------------
+    template <typename ValueT>
+    restore (ValueT&) -> restore<ValueT>;
+}