Add vector traits.

dune/matrix-vector/vectortraits.hh

+#ifndef DUNE_MATRIX_VECTOR_VECTORTRAITS_HH
+#define DUNE_MATRIX_VECTOR_VECTORTRAITS_HH
+
+#include <dune/common/fvector.hh>
+#include <dune/istl/bvector.hh>
+#include <dune/istl/multitypeblockvector.hh>
+
+namespace Dune {
+namespace MatrixVector {
+
+/** \brief Class to identify vector types and extract information
+ *
+ * Specialize this class for all types that can be used like a vector.
+ */
+template <class T>
+struct VectorTraits {
+  constexpr static bool isVector = false;
+};
+
+template <class K, int n>
+struct VectorTraits<FieldVector<K, n>> {
+  constexpr static bool isVector = true;
+};
+
+template <class Block>
+struct VectorTraits<BlockVector<Block>> {
+  constexpr static bool isVector = true;
+};
+
+} // end namespace MatrixVector
+} // end namespace Dune
+
+#endif // DUNE_MATRIX_VECTOR_VECTORTRAITS_HH