[mpfa][nodalindexset] pull out traits definition from property declaration

In order for a type to be completely typetag independent, the traits cannot
be declared inside the body of the property definition.

dumux/discretization/cellcentered/mpfa/dualgridindexset.hh

@@ -32,6 +32,30 @@
 
 namespace Dumux
 {
+/*!
+ * \ingroup CCMpfaDiscretization
+ * \brief Default traits to be used in conjuntion
+ *        with the dual grid nodal index set.
+ *
+ * \tparam GV The grid view type
+ */
+template<class GV>
+struct NodalIndexSetDefaultTraits
+{
+    using GridView = GV;
+    using GridIndexType = typename GV::IndexSet::IndexType;
+    using LocalIndexType = std::uint8_t;
+
+    //! per default, we use dynamic data containers (iv size unknown)
+    template< class T > using NodalScvDataStorage = std::vector< T >;
+    template< class T > using NodalScvfDataStorage = std::vector< T >;
+
+    //! store data on neighbors of scvfs in static containers if possible
+    template< class T >
+    using ScvfNeighborDataStorage = typename std::conditional_t< (int(GV::dimension)<int(GV::dimensionworld)),
+                                                                 std::vector< T >,
+                                                                 Dune::ReservedVector< T, 2 > >;
+};
 
 /*!
  * \ingroup CCMpfaDiscretization

dumux/discretization/cellcentered/mpfa/properties.hh

@@ -63,26 +63,10 @@ NEW_TYPE_TAG(CCMpfaModel, INHERITS_FROM(FiniteVolumeModel));
 //! Set the index set type used on the dual grid nodes
 SET_PROP(CCMpfaModel, DualGridNodalIndexSet)
 {
-    using GV = typename GET_PROP_TYPE(TypeTag, GridView);
-    static constexpr int dim = GV::dimension;
-    static constexpr int dimWorld = GV::dimensionworld;
 private:
-    struct Traits
-    {
-        using GridView = GV;
-        using GridIndexType = typename GV::IndexSet::IndexType;
-        using LocalIndexType = std::uint8_t;
-
-        //! per default, we use dynamic data containers (iv size unknown)
-        template< class T > using NodalScvDataStorage = std::vector< T >;
-        template< class T > using NodalScvfDataStorage = std::vector< T >;
-
-        //! store data on neighbors of scvfs in static containers if possible
-        template< class T >
-        using ScvfNeighborDataStorage = typename std::conditional_t< (dim<dimWorld),
-                                                                     std::vector< T >,
-                                                                     Dune::ReservedVector< T, 2 > >;
-    };
+    using GV = typename GET_PROP_TYPE(TypeTag, GridView);
+    using Traits = NodalIndexSetDefaultTraits< GV >;
+
 public:
     using type = CCMpfaDualGridNodalIndexSet< Traits >;
 };