From: Wolfgang Bangerth <bangerth@colostate.edu>
Date: Fri, 15 Dec 2023 05:04:07 +0000 (-0700)
Subject: Use std::variant instead of a hand-rolled version.
X-Git-Tag: relicensing~240^2
X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=refs%2Fpull%2F16355%2Fhead;p=dealii.git

Use std::variant instead of a hand-rolled version.
---

diff --git a/include/deal.II/fe/fe_values_base.h b/include/deal.II/fe/fe_values_base.h
index 3d56f8b895..7fe4802204 100644
--- a/include/deal.II/fe/fe_values_base.h
+++ b/include/deal.II/fe/fe_values_base.h
@@ -48,6 +48,7 @@
 #include <memory>
 #include <optional>
 #include <type_traits>
+#include <variant>
 
 DEAL_II_NAMESPACE_OPEN
 
@@ -1571,23 +1572,29 @@ protected:
       "FEValues::reinit() with an iterator type that allows to extract "
       "degrees of freedom, such as DoFHandler<dim,spacedim>::cell_iterator.");
 
+    /**
+     * Constructor. Creates an unusable object that is not associated with
+     * any cell at all.
+     */
+    CellIteratorContainer() = default;
+
     /**
      * Constructor.
      */
-    CellIteratorContainer();
+    CellIteratorContainer(
+      const typename Triangulation<dim, spacedim>::cell_iterator &cell);
 
     /**
      * Constructor.
      */
-    template <bool lda>
     CellIteratorContainer(
-      const TriaIterator<DoFCellAccessor<dim, spacedim, lda>> &cell);
+      const typename DoFHandler<dim, spacedim>::cell_iterator &cell);
 
     /**
      * Constructor.
      */
     CellIteratorContainer(
-      const typename Triangulation<dim, spacedim>::cell_iterator &cell);
+      const typename DoFHandler<dim, spacedim>::level_cell_iterator &cell);
 
     /**
      * Indicate whether FEValues::reinit() was called.
@@ -1628,9 +1635,16 @@ protected:
                                 Vector<IndexSet::value_type> &out) const;
 
   private:
-    std::optional<typename Triangulation<dim, spacedim>::cell_iterator> cell;
-    const DoFHandler<dim, spacedim> *dof_handler;
-    bool                             level_dof_access;
+    /**
+     * The cell in question, if one has been assigned to this object. The
+     * concrete data type can either be a Triangulation cell iterator, a
+     * DoFHandler cell iterator, or a DoFHandler level cell iterator.
+     */
+    std::optional<
+      std::variant<typename Triangulation<dim, spacedim>::cell_iterator,
+                   typename DoFHandler<dim, spacedim>::cell_iterator,
+                   typename DoFHandler<dim, spacedim>::level_cell_iterator>>
+      cell;
   };
 
   /**
@@ -1784,18 +1798,6 @@ private:
 
 /*---------------------- Inline functions: FEValuesBase ---------------------*/
 
-template <int dim, int spacedim>
-template <bool lda>
-inline FEValuesBase<dim, spacedim>::CellIteratorContainer::
-  CellIteratorContainer(
-    const TriaIterator<DoFCellAccessor<dim, spacedim, lda>> &cell)
-  : cell(cell)
-  , dof_handler(&cell->get_dof_handler())
-  , level_dof_access(lda)
-{}
-
-
-
 template <int dim, int spacedim>
 inline const FEValuesViews::Scalar<dim, spacedim> &
 FEValuesBase<dim, spacedim>::operator[](
diff --git a/source/fe/fe_values_base.cc b/source/fe/fe_values_base.cc
index 6120a4f9b0..c05c23618b 100644
--- a/source/fe/fe_values_base.cc
+++ b/source/fe/fe_values_base.cc
@@ -107,21 +107,27 @@ namespace internal
 
 /* ------------ FEValuesBase<dim,spacedim>::CellIteratorContainer ----------- */
 
+
 template <int dim, int spacedim>
-FEValuesBase<dim, spacedim>::CellIteratorContainer::CellIteratorContainer()
-  : cell()
-  , dof_handler(nullptr)
-  , level_dof_access(false)
+FEValuesBase<dim, spacedim>::CellIteratorContainer::CellIteratorContainer(
+  const typename Triangulation<dim, spacedim>::cell_iterator &cell)
+  : cell(cell)
 {}
 
 
 
 template <int dim, int spacedim>
 FEValuesBase<dim, spacedim>::CellIteratorContainer::CellIteratorContainer(
-  const typename Triangulation<dim, spacedim>::cell_iterator &cell)
+  const typename DoFHandler<dim, spacedim>::cell_iterator &cell)
+  : cell(cell)
+{}
+
+
+
+template <int dim, int spacedim>
+FEValuesBase<dim, spacedim>::CellIteratorContainer::CellIteratorContainer(
+  const typename DoFHandler<dim, spacedim>::level_cell_iterator &cell)
   : cell(cell)
-  , dof_handler(nullptr)
-  , level_dof_access(false)
 {}
 
 
@@ -141,7 +147,14 @@ operator typename Triangulation<dim, spacedim>::cell_iterator() const
 {
   Assert(is_initialized(), ExcNotReinited());
 
-  return cell.value();
+  // We can always convert to a tria iterator, regardless of which of
+  // the three types of cell we store.
+  return std::visit(
+    [](auto &cell_iterator) ->
+    typename Triangulation<dim, spacedim>::cell_iterator {
+      return cell_iterator;
+    },
+    cell.value());
 }
 
 
@@ -152,9 +165,17 @@ FEValuesBase<dim, spacedim>::CellIteratorContainer::n_dofs_for_dof_handler()
   const
 {
   Assert(is_initialized(), ExcNotReinited());
-  Assert(dof_handler != nullptr, ExcNeedsDoFHandler());
 
-  return dof_handler->n_dofs();
+  switch (cell.value().index())
+    {
+      case 1:
+        return std::get<1>(cell.value())->get_dof_handler().n_dofs();
+      case 2:
+        return std::get<2>(cell.value())->get_dof_handler().n_dofs();
+      default:
+        Assert(false, ExcNeedsDoFHandler());
+        return numbers::invalid_dof_index;
+    }
 }
 
 
@@ -167,20 +188,21 @@ FEValuesBase<dim, spacedim>::CellIteratorContainer::get_interpolated_dof_values(
   Vector<Number>           &out) const
 {
   Assert(is_initialized(), ExcNotReinited());
-  Assert(dof_handler != nullptr, ExcNeedsDoFHandler());
-
-  if (level_dof_access)
-    DoFCellAccessor<dim, spacedim, true>(&cell.value()->get_triangulation(),
-                                         cell.value()->level(),
-                                         cell.value()->index(),
-                                         dof_handler)
-      .get_interpolated_dof_values(in, out);
-  else
-    DoFCellAccessor<dim, spacedim, false>(&cell.value()->get_triangulation(),
-                                          cell.value()->level(),
-                                          cell.value()->index(),
-                                          dof_handler)
-      .get_interpolated_dof_values(in, out);
+
+  switch (cell.value().index())
+    {
+      case 1:
+        std::get<1>(cell.value())->get_interpolated_dof_values(in, out);
+        break;
+
+      case 2:
+        std::get<2>(cell.value())->get_interpolated_dof_values(in, out);
+        break;
+
+      default:
+        Assert(false, ExcNeedsDoFHandler());
+        break;
+    }
 }
 
 
@@ -192,21 +214,32 @@ FEValuesBase<dim, spacedim>::CellIteratorContainer::get_interpolated_dof_values(
   Vector<IndexSet::value_type> &out) const
 {
   Assert(is_initialized(), ExcNotReinited());
-  Assert(dof_handler != nullptr, ExcNeedsDoFHandler());
-  Assert(level_dof_access == false, ExcNotImplemented());
 
-  const DoFCellAccessor<dim, spacedim, false> cell_dofs(
-    &cell.value()->get_triangulation(),
-    cell.value()->level(),
-    cell.value()->index(),
-    dof_handler);
+  switch (cell.value().index())
+    {
+      case 1:
+        {
+          const typename DoFHandler<dim, spacedim>::cell_iterator cell =
+            std::get<1>(this->cell.value());
+
+          std::vector<types::global_dof_index> dof_indices(
+            cell->get_fe().n_dofs_per_cell());
+
+          cell->get_dof_indices(dof_indices);
 
-  std::vector<types::global_dof_index> dof_indices(
-    cell_dofs.get_fe().n_dofs_per_cell());
-  cell_dofs.get_dof_indices(dof_indices);
+          for (unsigned int i = 0; i < cell->get_fe().n_dofs_per_cell(); ++i)
+            out[i] = (in.is_element(dof_indices[i]) ? 1 : 0);
 
-  for (unsigned int i = 0; i < cell_dofs.get_fe().n_dofs_per_cell(); ++i)
-    out[i] = (in.is_element(dof_indices[i]) ? 1 : 0);
+          break;
+        }
+      case 2:
+        Assert(false, ExcNotImplemented());
+        break;
+
+      default:
+        Assert(false, ExcNeedsDoFHandler());
+        break;
+    }
 }