Add Dune::isNumber trait

dune/solvers/common/CMakeLists.txt

@@ -12,4 +12,5 @@ install(FILES
     resize.hh
     staticmatrixtools.hh
     tuplevector.hh
+    typetraits.hh
     DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}/dune/solvers/common)

dune/solvers/common/typetraits.hh

+#ifndef DUNE_SOLVERS_COMMON_TYPETRAITS_HH
+#define DUNE_SOLVERS_COMMON_TYPETRAITS_HH
+
+#include <type_traits>
+
+namespace Dune {
+template <typename T>
+struct isNumber
+    : public std::integral_constant<bool, std::is_arithmetic<T>::value> {};
+
+template <typename T>
+struct isNumber<std::complex<T>>
+    : public std::integral_constant<bool, isNumber<T>::value> {};
+}
+
+#endif