Make matrix/vector traversal termination work with proxy types

dune/fufem/backends/traversal.hh

@@ -8,6 +8,7 @@
 #include <functional>
 #include <variant>
 
+#include <dune/common/typetraits.hh>
 #include <dune/common/rangeutilities.hh>
 #include <dune/common/hybridutilities.hh>
 
@@ -115,7 +116,7 @@ namespace Dune::Fufem::Impl {
     template<class Entry, class FlatIndex>
     void operator()(Entry&& vector_i, FlatIndex i)
     {
-      if constexpr (Dune::IsNumber<std::decay_t<Entry>>::value)
+      if constexpr (Dune::IsNumber<typename Dune::AutonomousValueType<std::decay_t<Entry>>::type>::value)
         f_(vector_i, extendMultiIndex(index_, i));
       else
         Impl::forEachVectorEntry(vector_i, Dune::Fufem::Impl::RecursiveVectorVisitor(f_, extendMultiIndex(index_, i)));
@@ -141,7 +142,7 @@ namespace Dune::Fufem::Impl {
     template<class Entry, class FlatRowIndex, class FlatColIndex>
     void operator()(Entry&& matrix_ij, FlatRowIndex i, FlatColIndex j)
     {
-      if constexpr (Dune::IsNumber<std::decay_t<Entry>>::value)
+      if constexpr (Dune::IsNumber<typename Dune::AutonomousValueType<std::decay_t<Entry>>::type>::value)
         f_(matrix_ij, extendMultiIndex(rowIndex_, i), extendMultiIndex(colIndex_, j));
       else
         Impl::forEachMatrixEntry(matrix_ij, Dune::Fufem::Impl::RecursiveMatrixVisitor(f_, extendMultiIndex(rowIndex_, i), extendMultiIndex(colIndex_, j)));