[spaces...fem] hold shared_ptr of grid part (again)

This fixes a segfault, since after a copy of the space the backend_ would
still hold a reference to the grid_part_ of other which is not guaranteed
to still exist. Thus we would need to make a copy of backend_ (not possible
with dune-fem) or create a new backend_ (which would mathematically
hopefully be a copy, but we do not know about dune-fems internals so we can
not be sure) or again hold a shared_ptr of the backend_ and the grid_part_
and the grid_view_, which I opted for.

dune/gdt/playground/spaces/discontinuouslagrange/fem.hh

@@ -106,11 +106,11 @@ public:
   typedef Dune::Stuff::LA::SparsityPatternDefault PatternType;
 
   FemBased(GridPartType gridP)
-    : gridPart_(gridP)
-    , gridView_(gridPart_.gridView())
-    , backend_(std::make_shared<BackendType>(gridPart_))
-    , mapper_(std::make_shared<MapperType>(backend_->blockMapper()))
-    , communicator_(CommunicationChooserType::create(gridView_))
+    : gridPart_(new GridPartType(gridP))
+    , gridView_(new GridViewType(gridPart_->gridView()))
+    , backend_(new BackendType(*gridPart_))
+    , mapper_(new MapperType(backend_->blockMapper()))
+    , communicator_(CommunicationChooserType::create(*gridView_))
   {
   }
 
@@ -132,12 +132,12 @@ public:
 
   const GridPartType& grid_part() const
   {
-    return gridPart_;
+    return *gridPart_;
   }
 
   const GridViewType& grid_view() const
   {
-    return gridView_;
+    return *gridView_;
   }
 
   const BackendType& backend() const
@@ -162,8 +162,8 @@ public:
   }
 
 private:
-  GridPartType gridPart_;
-  const GridViewType gridView_;
+  std::shared_ptr<GridPartType> gridPart_;
+  const std::shared_ptr<const GridViewType> gridView_;
   const std::shared_ptr<const BackendType> backend_;
   const std::shared_ptr<const MapperType> mapper_;
   mutable std::shared_ptr<CommunicatorType> communicator_;

dune/gdt/spaces/continuouslagrange/fem.hh

@@ -109,47 +109,29 @@ public:
   typedef Dune::Stuff::LA::SparsityPatternDefault PatternType;
 
   FemBased(GridPartType gridP)
-    : gridPart_(gridP)
-    , gridView_(gridPart_.gridView())
-    , backend_(std::make_shared<const BackendType>(const_cast<GridPartType&>(gridPart_)))
-    , mapper_(backend_->blockMapper())
-    , communicator_(CommunicationChooserType::create(gridView_))
+    : gridPart_(new GridPartType(gridP))
+    , gridView_(new GridViewType(gridPart_->gridView()))
+    , backend_(new BackendType(*gridPart_))
+    , mapper_(new MapperType(backend_->blockMapper()))
+    , communicator_(CommunicationChooserType::create(*gridView_))
   {
   }
 
-  //! explicitly defaulted ctor was still implcitly deleted although no non-static members have reference type
-  FemBased(const ThisType& other)
-    : gridPart_(other.gridPart_)
-    , gridView_(other.gridView_)
-    , backend_(other.backend_)
-    , mapper_(other.mapper_)
-    , communicator_(DSC::make_unique<CommunicatorType>(*other.communicator_))
-  {
-    assert(communicator_);
-  }
 
-  //! explicitly defaulted ctor was still implcitly deleted although no non-static members have reference type
-  FemBased(ThisType&& other)
-    : gridPart_(other.gridPart_)
-    , gridView_(other.gridView_)
-    , backend_(other.backend_)
-    , mapper_(other.mapper_)
-    , communicator_(std::move(other.communicator_))
-  {
-    assert(communicator_);
-  }
+  FemBased(const ThisType& other) = default;
+  FemBased(ThisType&& source) = default;
 
   ThisType& operator=(const ThisType& other) = delete;
   ThisType& operator=(ThisType&& source) = delete;
 
   const GridPartType& grid_part() const
   {
-    return gridPart_;
+    return *gridPart_;
   }
 
   const GridViewType& grid_view() const
   {
-    return gridView_;
+    return *gridView_;
   }
 
   const BackendType& backend() const
@@ -159,7 +141,7 @@ public:
 
   const MapperType& mapper() const
   {
-    return mapper_;
+    return *mapper_;
   }
 
   BaseFunctionSetType base_function_set(const EntityType& entity) const
@@ -174,11 +156,11 @@ public:
   }
 
 private:
-  const GridPartType gridPart_;
-  const GridViewType gridView_;
+  std::shared_ptr<GridPartType> gridPart_;
+  const std::shared_ptr<const GridViewType> gridView_;
   const std::shared_ptr<const BackendType> backend_;
-  const MapperType mapper_;
-  mutable std::unique_ptr<CommunicatorType> communicator_;
+  const std::shared_ptr<const MapperType> mapper_;
+  mutable std::shared_ptr<CommunicatorType> communicator_;
 }; // class FemBased< ..., 1 >