From: Wolfgang Bangerth <bangerth@colostate.edu>
Date: Thu, 21 Jan 2021 18:51:23 +0000 (-0700)
Subject: Hide the ability to create ReferenceCell objects from users.
X-Git-Tag: v9.3.0-rc1~583^2~2
X-Git-Url: https://gitweb.dealii.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=6871ff499ed6eba024a4b25191af3db7521784eb;p=dealii.git

Hide the ability to create ReferenceCell objects from users.
---

diff --git a/include/deal.II/grid/reference_cell.h b/include/deal.II/grid/reference_cell.h
index 12a6b8cd40..f0bcfeca43 100644
--- a/include/deal.II/grid/reference_cell.h
+++ b/include/deal.II/grid/reference_cell.h
@@ -42,6 +42,29 @@ class ScalarPolynomialsBase;
  */
 namespace ReferenceCell
 {
+  class Type;
+
+  namespace internal
+  {
+    /**
+     * A helper function to create a ReferenceCell::Type object from an
+     * integer. ReferenceCell::Type objects are "singletons" (actually,
+     * "multitons" -- there are multiple, but they are only a handful and
+     * these are all that can be used). What is then necessary is to
+     * have a way to create these with their internal id to distinguish
+     * the few possible ones in existence. We could do this via a public
+     * constructor of ReferenceCell::Type, but that would allow users to
+     * create ones outside the range we envision, and we don't want to do
+     * that. Rather, the constructor that takes an integer is made `private`
+     * but we have this one function in an internal namespace that is a friend
+     * of the class and can be used to create the objects.
+     */
+    Type
+    make_reference_cell_from_int(const std::uint8_t kind);
+  } // namespace internal
+
+
+
   /**
    * A type that describes the kinds of reference cells that can be used.
    * This includes quadrilaterals and hexahedra (i.e., "hypercubes"),
@@ -66,12 +89,6 @@ namespace ReferenceCell
      */
     constexpr Type();
 
-    /**
-     * Constructor.
-     */
-    constexpr Type(const std::uint8_t kind);
-
-
     /**
      * Return true if the object is a Vertex, Line, Quad, or Hex.
      */
@@ -181,6 +198,21 @@ namespace ReferenceCell
      * The variable that stores what this object actually corresponds to.
      */
     std::uint8_t kind;
+
+    /**
+     * Constructor. This is the constructor used to create the different
+     * `static` member variables of this class. It is `private` but can
+     * be called by a function in an internal namespace that is a `friend`
+     * of this class.
+     */
+    constexpr Type(const std::uint8_t kind);
+
+    /**
+     * A kind of constructor -- not quite private because it can be
+     * called by anyone, but at least hidden in an internal namespace.
+     */
+    friend Type
+    internal::make_reference_cell_from_int(const std::uint8_t);
   };
 
 
diff --git a/source/distributed/tria_base.cc b/source/distributed/tria_base.cc
index a5cb108513..75b0730d1d 100644
--- a/source/distributed/tria_base.cc
+++ b/source/distributed/tria_base.cc
@@ -309,7 +309,8 @@ namespace parallel
     // transform back and store result
     this->reference_cell_types.clear();
     for (const auto &i : reference_cell_types_ui)
-      this->reference_cell_types.emplace_back(static_cast<std::uint8_t>(i));
+      this->reference_cell_types.emplace_back(
+        ReferenceCell::internal::make_reference_cell_from_int(i));
   }
 
 
diff --git a/source/grid/reference_cell.cc b/source/grid/reference_cell.cc
index 9e473a0592..f9b9fecb15 100644
--- a/source/grid/reference_cell.cc
+++ b/source/grid/reference_cell.cc
@@ -30,17 +30,31 @@
 
 DEAL_II_NAMESPACE_OPEN
 
+
 namespace ReferenceCell
 {
-  const Type Type::Vertex  = Type(0);
-  const Type Type::Line    = Type(1);
-  const Type Type::Tri     = Type(2);
-  const Type Type::Quad    = Type(3);
-  const Type Type::Tet     = Type(4);
-  const Type Type::Pyramid = Type(5);
-  const Type Type::Wedge   = Type(6);
-  const Type Type::Hex     = Type(7);
-  const Type Type::Invalid = Type(static_cast<std::uint8_t>(-1));
+  namespace internal
+  {
+    dealii::ReferenceCell::Type
+    make_reference_cell_from_int(const std::uint8_t kind)
+    {
+      // Call the private constructor, which we can from here because this
+      // function is a 'friend'.
+      return dealii::ReferenceCell::Type(kind);
+    }
+  } // namespace internal
+
+
+  const Type Type::Vertex  = internal::make_reference_cell_from_int(0);
+  const Type Type::Line    = internal::make_reference_cell_from_int(1);
+  const Type Type::Tri     = internal::make_reference_cell_from_int(2);
+  const Type Type::Quad    = internal::make_reference_cell_from_int(3);
+  const Type Type::Tet     = internal::make_reference_cell_from_int(4);
+  const Type Type::Pyramid = internal::make_reference_cell_from_int(5);
+  const Type Type::Wedge   = internal::make_reference_cell_from_int(6);
+  const Type Type::Hex     = internal::make_reference_cell_from_int(7);
+  const Type Type::Invalid =
+    internal::make_reference_cell_from_int(static_cast<std::uint8_t>(-1));
 
 
   template <int dim, int spacedim>