[common] Add Python-like enumerate function for ranges

dumux/common/CMakeLists.txt

@@ -17,6 +17,7 @@ doubleexpintegrationconstants.hh
 doubleexpintegrator.hh
 dumuxmessage.hh
 entitymap.hh
+enumerate.hh
 exceptions.hh
 fixedlengthspline_.hh
 fvproblem.hh

dumux/common/enumerate.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 3 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 A Python-like enumerate function
+ */
+
+#ifndef DUMUX_COMMON_ENUMERATE_HH
+#define DUMUX_COMMON_ENUMERATE_HH
+
+#include <tuple>
+
+namespace Dumux {
+
+/*!
+ * \brief A Python-like enumerate function
+ * \param iterable Some iterable type with begin/end (e.g. std::vector)
+ * \note From Nathan Reed (CC BY 4.0): http://reedbeta.com/blog/python-like-enumerate-in-cpp17/
+ *
+ * Usage example: for (const auto& [i, item] : enumerate(list))
+ */
+template <typename Range,
+          typename RangeIterator = decltype(std::begin(std::declval<Range>())),
+          typename = decltype(std::end(std::declval<Range>()))>
+constexpr auto enumerate(Range&& iterable)
+{
+    struct Iterator
+    {
+        std::size_t i;
+        RangeIterator iter;
+        bool operator != (const Iterator & other) const { return iter != other.iter; }
+        void operator ++ () { ++i; ++iter; }
+        auto operator * () const { return std::tie(i, *iter); }
+    };
+
+    struct Iteratable
+    {
+        Range iterable;
+        auto begin() { return Iterator{ 0, std::begin(iterable) }; }
+        auto end() { return Iterator{ 0, std::end(iterable) }; }
+    };
+
+    return Iteratable{ std::forward<Range>(iterable) };
+}
+
+} // end namespace Dumux
+
+#endif