[operators] keep a copy of the grid view

dune/gdt/operators/ipdg-flux-reconstruction.hh

@@ -54,7 +54,7 @@ public:
   using E = XT::Grid::extract_entity_t<AssemblyGridViewType>;
   static const constexpr size_t d = RGV::dimension;
 
-  IpdgFluxReconstructionOperator(const AssemblyGridViewType& assembly_grid_view,
+  IpdgFluxReconstructionOperator(AssemblyGridViewType assembly_grid_view,
                                  const SourceSpaceType& src_spc,
                                  const RangeSpaceType& rng_spc,
                                  const XT::Functions::GridFunctionInterface<E>& diffusion_factor,
@@ -297,7 +297,7 @@ public:
   } // ... apply(...)
 
 private:
-  const AssemblyGridViewType& assembly_grid_view_;
+  const AssemblyGridViewType assembly_grid_view_;
   const SourceSpaceType& source_space_;
   const RangeSpaceType& range_space_;
   const XT::Functions::GridFunctionInterface<E>& diffusion_factor_;

dune/gdt/operators/oswald-interpolation.hh

@@ -59,7 +59,7 @@ public:
   /**
    * \param boundary_info To determine the Dirichlet boundary DoFs on which to set the range to zero.
    */
-  OswaldInterpolationOperator(const AssemblyGridViewType& assembly_grid_view,
+  OswaldInterpolationOperator(AssemblyGridViewType assembly_grid_view,
                               const SourceSpaceType& src_spc,
                               const RangeSpaceType& rng_spc,
                               const XT::Grid::BoundaryInfo<I>& boundary_info)
@@ -194,7 +194,7 @@ public:
   } // ... apply(...)
 
 private:
-  const AssemblyGridViewType& assembly_grid_view_;
+  const AssemblyGridViewType assembly_grid_view_;
   const SourceSpaceType& source_space_;
   const RangeSpaceType& range_space_;
   const XT::Common::ConstStorageProvider<XT::Grid::BoundaryInfo<I>> boundary_info_;