extract signature directly from gridfunction

dune/curvedsurfacegrid/gridfamily.hh

@@ -33,7 +33,7 @@ namespace Dune
     template< class GF >
     struct DimRange
     {
-      using SigTraits = Functions::SignatureTraits<typename GF::Signature>;
+      using SigTraits = Functions::SignatureTraits<GF>;
       using Range = typename SigTraits::RawRange;
       static const int value = Range::size();
     };
@@ -44,7 +44,7 @@ namespace Dune
       using EntitySet = typename GF::EntitySet;
       using LocalContext = typename EntitySet::Element;
 
-      using Range = typename Functions::SignatureTraits<typename GF::Signature>::Range;
+      using Range = typename Functions::SignatureTraits<GF>::Range;
       using LocalSignature = Range(typename EntitySet::LocalCoordinate);
 
       static const bool value = Functions::Concept::isDifferentiableLocalFunction<LF,LocalSignature,LocalContext,Functions::LocalDerivativeTraits<EntitySet>::template Traits>();
@@ -62,7 +62,7 @@ namespace Dune
         using HostGrid = GridOf_t<GF>;
 
         using GridFunction = GF;
-        using LocalFunction = std::decay_t<decltype(localFunction(std::declval<GF>()))>;
+        using LocalFunction = std::decay_t<decltype(localFunction(std::declval<GF const&>()))>;
 
         static const bool differentiableLocalFunction = DifferentiableLocalFunction<GF, LocalFunction>::value;