From ab67ed22932f45e353b2c71ad4080e83e85f10d8 Mon Sep 17 00:00:00 2001
From: Jean-Paul Pelteret <jppelteret@gmail.com>
Date: Wed, 17 Apr 2019 22:27:00 +0200
Subject: [PATCH] Add ProductType for SD::Expression class.

This is the first step towards support of SD::Expression within the
Tensor and SymmetricTensor classes.
---
 include/deal.II/differentiation/sd.h          |   1 +
 .../sd/symengine_product_types.h              | 121 ++++++++++++++++++
 2 files changed, 122 insertions(+)
 create mode 100644 include/deal.II/differentiation/sd/symengine_product_types.h

diff --git a/include/deal.II/differentiation/sd.h b/include/deal.II/differentiation/sd.h
index 2050e6a509..5039e8a4a2 100644
--- a/include/deal.II/differentiation/sd.h
+++ b/include/deal.II/differentiation/sd.h
@@ -23,6 +23,7 @@
 #  include <deal.II/differentiation/sd/symengine_math.h>
 #  include <deal.II/differentiation/sd/symengine_number_traits.h>
 #  include <deal.II/differentiation/sd/symengine_number_types.h>
+#  include <deal.II/differentiation/sd/symengine_product_types.h>
 #  include <deal.II/differentiation/sd/symengine_scalar_operations.h>
 #  include <deal.II/differentiation/sd/symengine_types.h>
 #  include <deal.II/differentiation/sd/symengine_utilities.h>
diff --git a/include/deal.II/differentiation/sd/symengine_product_types.h b/include/deal.II/differentiation/sd/symengine_product_types.h
new file mode 100644
index 0000000000..06d78aa6c5
--- /dev/null
+++ b/include/deal.II/differentiation/sd/symengine_product_types.h
@@ -0,0 +1,121 @@
+// ---------------------------------------------------------------------
+//
+// Copyright (C) 2019 by the deal.II authors
+//
+// This file is part of the deal.II library.
+//
+// The deal.II library is free software; you can use it, redistribute
+// it, and/or modify it under the terms of the GNU Lesser General
+// Public License as published by the Free Software Foundation; either
+// version 2.1 of the License, or (at your option) any later version.
+// The full text of the license can be found in the file LICENSE at
+// the top level of the deal.II distribution.
+//
+// ---------------------------------------------------------------------
+
+#ifndef dealii_differentiation_sd_symengine_product_types_h
+#define dealii_differentiation_sd_symengine_product_types_h
+
+#include <deal.II/base/config.h>
+
+#ifdef DEAL_II_WITH_SYMENGINE
+
+
+#  include <deal.II/base/template_constraints.h>
+
+#  include <deal.II/differentiation/sd/symengine_number_types.h>
+
+#  include <boost/type_traits.hpp>
+
+#  include <type_traits>
+
+
+DEAL_II_NAMESPACE_OPEN
+
+
+template <>
+struct EnableIfScalar<Differentiation::SD::Expression>
+{
+  typedef Differentiation::SD::Expression type;
+};
+
+
+namespace internal
+{
+  namespace SD
+  {
+    /**
+     * A more general implementation of product types.
+     * There are so many permutation of admissible operations
+     * that getting the compiler to determine the valid
+     * combinations using template metaprogramming makes
+     * more sense than manually maintaining the list by
+     * hand.
+     *
+     * This class is a workaround for issue of non-deduction
+     * of types in template partial specializations that
+     * would otherwise occur if trying to directly implement
+     * these as specializations of the ProductTypeImpl class
+     * itself.
+     *
+     * @author Jean-Paul Pelteret, 2019
+     */
+    template <typename T, typename U, typename V = void>
+    struct GeneralProductTypeImpl;
+
+    template <typename T>
+    struct GeneralProductTypeImpl<
+      T,
+      Differentiation::SD::Expression,
+      typename std::enable_if<std::is_arithmetic<T>::value>::type>
+    {
+      typedef Differentiation::SD::Expression type;
+    };
+
+    template <typename T>
+    struct GeneralProductTypeImpl<
+      T,
+      Differentiation::SD::Expression,
+      typename std::enable_if<
+        boost::is_complex<T>::value &&
+        std::is_arithmetic<typename T::value_type>::value>::type>
+    {
+      typedef Differentiation::SD::Expression type;
+    };
+
+  } // namespace SD
+
+
+  template <>
+  struct ProductTypeImpl<Differentiation::SD::Expression,
+                         Differentiation::SD::Expression>
+  {
+    typedef Differentiation::SD::Expression type;
+  };
+
+
+  template <typename T>
+  struct ProductTypeImpl<T, Differentiation::SD::Expression>
+  {
+    typedef
+      typename SD::GeneralProductTypeImpl<T,
+                                          Differentiation::SD::Expression>::type
+        type;
+  };
+
+  template <typename T>
+  struct ProductTypeImpl<Differentiation::SD::Expression, T>
+  {
+    typedef
+      typename SD::GeneralProductTypeImpl<T,
+                                          Differentiation::SD::Expression>::type
+        type;
+  };
+
+} // namespace internal
+
+DEAL_II_NAMESPACE_CLOSE
+
+#endif // DEAL_II_WITH_SYMENGINE
+
+#endif
-- 
2.39.5