strongdef: add simple thin value wrapper type

useful for strong typesafe typedefs.

Makefile.am

@@ -286,6 +286,8 @@ UTIL_FILES   =			\
     string.hpp			\
     stringid.cpp		\
     stringid.hpp		\
+    strongdef.cpp		\
+    strongdef.hpp		\
     tap.cpp			\
     tap.hpp			\
     tap.ipp			\

strongdef.cpp

@@ -0,0 +1,26 @@
+/*
+ * 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 2015 Danny Robson <danny@nerdcruft.net>
+ */
+
+#include "./strongdef.hpp"
+
+using util::strongdef;
+
+
+///////////////////////////////////////////////////////////////////////////////
+// This instantiation is not meant to be exported, only being used as a local
+// compilation error canary.
+
+template struct util::strongdef<unsigned>;

strongdef.hpp

@@ -0,0 +1,49 @@
+/*
+ * 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 2015 Danny Robson <danny@nerdcruft.net>
+ */
+
+#ifndef __UTIL_STRONGDEF_HPP
+#define __UTIL_STRONGDEF_HPP
+
+namespace util {
+    /// A transparent wrapper around a (typically lightweight) type for the
+    /// purposes of overload disambiguation. It acts like a typesafe typedef.
+    template <typename T>
+    struct strongdef {
+    public:
+        using value_type = T;
+
+        constexpr strongdef () = default;
+        constexpr explicit strongdef (T _data):
+            data (_data)
+        { ; }
+
+        strongdef& operator= (const strongdef &rhs)
+        { data = rhs.data; return *this; }
+
+        strongdef& operator= (const T &rhs)
+        { data = rhs;      return *this; }
+
+        operator const T& (void) const { return data; }
+        operator       T& (void)       { return data; }
+
+        bool operator== (const strongdef &rhs) const
+        { return data == rhs.data; }
+
+        T data;
+    };
+}
+
+#endif