[common] implement id pair class

frackit/common/CMakeLists.txt

@@ -2,6 +2,7 @@ install(FILES
 extractctype.hh
 extractdimension.hh
 id.hh
+idpair.hh
 math.hh
 promotedtype.hh
 typetraits.hh

frackit/common/idpair.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 class to define pairs of ids.
+ */
+#ifndef FRACKIT_ID_PAIR_HH
+#define FRACKIT_ID_PAIR_HH
+
+#include <type_traits>
+
+#include "id.hh"
+
+namespace Frackit {
+
+/*!
+ * \brief Simple class to define pairs of ids.
+ */
+class IdPair
+{
+public:
+    //! Default constructor
+    IdPair() = default;
+
+    /*!
+     * \brief Construction from indices.
+     */
+    explicit IdPair(std::size_t id1, std::size_t id2)
+    : first_(id1)
+    , second_(id2)
+    {}
+
+    /*!
+     * \brief Construction from ids.
+     */
+    explicit IdPair(Id id1, Id id2)
+    : first_(id1)
+    , second_(id2)
+    {}
+
+    /*!
+     * \brief Retrieve the first id.
+     */
+    const Id& first() const { return first_; }
+
+    /*!
+     * \brief Retrieve the second id.
+     */
+    const Id& second() const { return second_; }
+private:
+    Id first_;
+    Id second_;
+};
+
+} // end namespace Frackit
+
+#endif // FRACKIT_ID_PAIR_HH