From 66b39bdf41b23c960eccfa42d76e6297384ff384 Mon Sep 17 00:00:00 2001
From: Wolfgang Bangerth <bangerth@colostate.edu>
Date: Sun, 24 Oct 2021 19:53:51 -0600
Subject: [PATCH] Make Patch<0,spacedim>::reference_cell const.

---
 include/deal.II/base/data_out_base.h | 6 ++++--
 source/base/data_out_base.cc         | 5 ++++-
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/include/deal.II/base/data_out_base.h b/include/deal.II/base/data_out_base.h
index 4a049fdbae..6d8e17febd 100644
--- a/include/deal.II/base/data_out_base.h
+++ b/include/deal.II/base/data_out_base.h
@@ -472,9 +472,11 @@ namespace DataOutBase
     bool points_are_available;
 
     /**
-     * Reference-cell type of the underlying cell of this patch.
+     * Reference-cell type of the underlying cell of this patch. Since for
+     * zero-dimensional objects, a patch can only refer to a vertex, this
+     * field is always equal to ReferenceCells::Vertex and can not be changed.
      */
-    ReferenceCell reference_cell;
+    static const ReferenceCell reference_cell;
 
     /**
      * Default constructor. Sets #points_are_available
diff --git a/source/base/data_out_base.cc b/source/base/data_out_base.cc
index 15ea5df1c6..c5460d360b 100644
--- a/source/base/data_out_base.cc
+++ b/source/base/data_out_base.cc
@@ -2066,11 +2066,14 @@ namespace DataOutBase
   template <int spacedim>
   unsigned int Patch<0, spacedim>::n_subdivisions = 1;
 
+  template <int spacedim>
+  const ReferenceCell Patch<0, spacedim>::reference_cell =
+    ReferenceCells::Vertex;
+
   template <int spacedim>
   Patch<0, spacedim>::Patch()
     : patch_index(no_neighbor)
     , points_are_available(false)
-    , reference_cell(ReferenceCells::get_hypercube<0>())
   {
     Assert(spacedim <= 3, ExcNotImplemented());
   }
-- 
2.39.5