From f445925e2b0be822b594da1bfcca70ecbfdbc1f4 Mon Sep 17 00:00:00 2001
From: Wolfgang Bangerth <bangerth@colostate.edu>
Date: Mon, 25 Oct 2021 16:17:58 -0600
Subject: [PATCH] Provide input and output operators for ReferenceCell.

---
 include/deal.II/grid/reference_cell.h | 28 +++++++++++++++++
 source/grid/reference_cell.cc         | 45 +++++++++++++++++++++++++++
 2 files changed, 73 insertions(+)

diff --git a/include/deal.II/grid/reference_cell.h b/include/deal.II/grid/reference_cell.h
index 190f3d3fef..d34ccd09e4 100644
--- a/include/deal.II/grid/reference_cell.h
+++ b/include/deal.II/grid/reference_cell.h
@@ -25,6 +25,8 @@
 #include <deal.II/base/tensor.h>
 #include <deal.II/base/utilities.h>
 
+#include <iosfwd>
+#include <string>
 
 DEAL_II_NAMESPACE_OPEN
 
@@ -582,9 +584,35 @@ private:
    */
   friend DEAL_II_CONSTEXPR ReferenceCell
   internal::ReferenceCell::make_reference_cell_from_int(const std::uint8_t);
+
+  friend std::ostream &
+  operator<<(std::ostream &out, const ReferenceCell &reference_cell);
+
+  friend std::istream &
+  operator>>(std::istream &in, ReferenceCell &reference_cell);
 };
 
 
+/**
+ * Output operator that writes the @p reference_cell object to the stream
+ * in a text format in which the object is represented by an integer. The
+ * details of which integer value represents each kind of reference cell
+ * is unimportant and consequently not specified. If you want a string
+ * representation of what a ReferenceCell is, use ReferenceCell::to_string().
+ */
+std::ostream &
+operator<<(std::ostream &out, const ReferenceCell &reference_cell);
+
+/**
+ * Input operator that reads the @p reference_cell object from the stream
+ * in a text format in which the object is represented by an integer. Which
+ * specific integer value represents which reference cell is unspecified,
+ * but the function uses the same translation as the corresponding
+ * output `operator<<`.
+ */
+std::istream &
+operator>>(std::istream &in, ReferenceCell &reference_cell);
+
 
 inline constexpr ReferenceCell::ReferenceCell(const std::uint8_t kind)
   : kind(kind)
diff --git a/source/grid/reference_cell.cc b/source/grid/reference_cell.cc
index a730be32c1..b8f518ef62 100644
--- a/source/grid/reference_cell.cc
+++ b/source/grid/reference_cell.cc
@@ -30,6 +30,7 @@
 #include <deal.II/grid/reference_cell.h>
 #include <deal.II/grid/tria.h>
 
+#include <iostream>
 #include <memory>
 
 DEAL_II_NAMESPACE_OPEN
@@ -455,6 +456,50 @@ ReferenceCell::vtk_lagrange_type() const
   return VTKCellType::VTK_INVALID;
 }
 
+
+
+std::ostream &
+operator<<(std::ostream &out, const ReferenceCell &reference_cell)
+{
+  AssertThrow(out, ExcIO());
+
+  // Output as an integer to avoid outputting it as a character with
+  // potentially non-printing value:
+  out << static_cast<unsigned int>(reference_cell.kind);
+  return out;
+}
+
+
+
+std::istream &
+operator>>(std::istream &in, ReferenceCell &reference_cell)
+{
+  AssertThrow(in, ExcIO());
+
+  // Read the information as an integer and convert it to the correct type
+  unsigned int value;
+  in >> value;
+  reference_cell.kind = static_cast<decltype(reference_cell.kind)>(value);
+
+  // Ensure that the object we read is valid
+  Assert(
+    (reference_cell == ReferenceCells::Vertex) ||
+      (reference_cell == ReferenceCells::Line) ||
+      (reference_cell == ReferenceCells::Triangle) ||
+      (reference_cell == ReferenceCells::Quadrilateral) ||
+      (reference_cell == ReferenceCells::Tetrahedron) ||
+      (reference_cell == ReferenceCells::Hexahedron) ||
+      (reference_cell == ReferenceCells::Wedge) ||
+      (reference_cell == ReferenceCells::Pyramid) ||
+      (reference_cell == ReferenceCells::Invalid),
+    ExcMessage(
+      "The reference cell kind just read does not correspond to one of the valid choices. There must be an error."));
+
+  return in;
+}
+
+
+
 #include "reference_cell.inst"
 
 DEAL_II_NAMESPACE_CLOSE
-- 
2.39.5