[common] introduce id class

frackit/common/CMakeLists.txt

 install(FILES
 extractctype.hh
 extractdimension.hh
+id.hh
 math.hh
 promotedtype.hh
 DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/frackit/common)

frackit/common/id.hh

+// -*- mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+// vi: set et ts=4 sw=4 sts=4:
+/*****************************************************************************
+ *   See the file COPYING for full copying permissions.                      *
+ *                                                                           *
+ *   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, see <http://www.gnu.org/licenses/>.   *
+ *****************************************************************************/
+/*!
+ * \file
+ * \brief Simple wrapper class to define ids/indices.
+ */
+#ifndef FRACKIT_ID_HH
+#define FRACKIT_ID_HH
+
+namespace Frackit {
+
+/*!
+ * \brief Simple wrapper class to define ids/indices.
+ *        This can be used wherever indices are passed
+ *        to interfaces to avoid implicit conversion of
+ *        function arguments.
+ */
+class Id
+{
+public:
+    /*!
+     * \brief Construction from an index.
+     */
+    explicit Id(std::size_t id)
+    : id_(id)
+    {}
+
+    /*!
+     * \brief Retrieve the index.
+     */
+    std::size_t get() const
+    { return id_; }
+
+private:
+    std::size_t id_;
+};
+
+} // end namespace Frackit
+
+#endif // FRACKIT_ID_HH