[common] Add a helper to create named equality-comparable tags

dumux/common/CMakeLists.txt

@@ -40,6 +40,7 @@ splinecommon_.hh
 staggeredfvproblem.hh
 start.hh
 tabulated2dfunction.hh
+tag.hh
 timeloop.hh
 timemanager.hh
 valgrind.hh

dumux/common/tag.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
+ * \ingroup Common
+ * \brief Helper class to create (named and comparable) tagged types
+ */
+#ifndef DUMUX_COMMON_TAG_HH
+#define DUMUX_COMMON_TAG_HH
+
+#include <sstream>
+#include <ostream>
+#include <type_traits>
+#include <dune/common/classname.hh>
+#include <dumux/common/typetraits/isvalid.hh>
+
+namespace Dumux::Utility {
+
+/*!
+ * \ingroup Common
+ * \brief Helper class to create (named and comparable) tagged types
+ * Tags any given type. The tagged type is equality comparable and can be written to streams.
+ * A custom name can be provided by implementing the `name()` member function.
+ */
+template<class T>
+struct Tag {};
+
+//! Tags are equality comparable and return true if the tagged types are equal
+template<class T1, class T2>
+inline constexpr bool operator==(Tag<T1>, Tag<T2>)
+{ return std::is_same_v<T1, T2>; }
+
+template<class T1, class T2>
+inline constexpr bool operator!=(Tag<T1>, Tag<T2>)
+{ return !std::is_same_v<T1, T2>; }
+
+namespace Detail {
+constexpr auto hasName = isValid([](auto&& t) -> decltype(t.name(), void()) {});
+} // end namespace Detail
+
+//! Return the class name of the tagged type calling t.name()
+template<class T, std::enable_if_t<std::is_base_of_v<Tag<T>, T>, int> = 0>
+auto operator<<(std::ostream& os, const T& t)
+-> std::enable_if_t<decltype(Detail::hasName(t))::value, std::ostream&>
+{ os << t.name(); return os; }
+
+//! Return the class name of the tagged type calling Dune::className if t.name() doesn't exist
+template<class T, std::enable_if_t<std::is_base_of_v<Tag<T>, T>, int> = 0>
+auto operator<<(std::ostream& os, const T& t)
+-> std::enable_if_t<!decltype(Detail::hasName(t))::value, std::ostream&>
+{
+    const auto fullName = Dune::className<T>();
+
+    // strip all namespace qualifiers
+    const auto pos = fullName.rfind("::");
+    const auto name = pos != std::string::npos ? fullName.substr(pos+2) : fullName;
+
+    os << name;
+    return os;
+}
+
+} // end namespace Dumux::Utility
+
+#endif

test/common/CMakeLists.txt

@@ -9,3 +9,4 @@ add_subdirectory(typetraits)
 
 dumux_add_test(SOURCES test_partial.cc LABELS unit)
 dumux_add_test(SOURCES test_enumerate.cc LABELS unit)
+dumux_add_test(SOURCES test_tag.cc LABELS unit)

test/common/test_tag.cc

+#include <config.h>
+#include <iostream>
+
+#include <dune/common/exceptions.hh>
+
+#include <dumux/common/tag.hh>
+
+namespace Dumux {
+
+struct T1 : public Utility::Tag<T1> {};
+struct T2 : public Utility::Tag<T2> { std::string name() const { return "customname_t2"; }};
+
+} // end namespace Dumux
+
+int main(int argc, char* argv[])
+{
+    using namespace Dumux;
+
+    T1 t11, t12;
+    T2 t2;
+
+    static_assert(t11 == t12, "Same tags not equal!");
+    static_assert(t11 != t2, "Different tags should not be equal!");
+
+    {
+        std::stringstream s; s << t11;
+        if (s.str() != "T1")
+            DUNE_THROW(Dune::Exception, "Wrong name: " << s.str() << ", expected: T1.");
+    }{
+        std::stringstream s; s << t2;
+        if (s.str() != "customname_t2")
+            DUNE_THROW(Dune::Exception, "Wrong name: " << s.str() << ", expected: customname_t2.");
+    }
+
+    return 0;
+}