Merge pull request #3389 from lindsayad/tensor-traits

Add TensorTraits

Author: roystgnr

include/base/libmesh_common.h

@@ -697,6 +697,13 @@ inline Tnew libmesh_cast_int (Told oldvar)
   return cast_int<Tnew>(oldvar);
 }
 
+/**
+ * This is a helper variable template for cases when we want to use a default compile-time
+ * error with constexpr-based if conditions. The templating delays the triggering
+ * of the static assertion until the template is instantiated.
+ */
+template <class T>
+constexpr std::false_type always_false{};
 
 // build a integer representation of version
 #define LIBMESH_VERSION_ID(major,minor,patch) (((major) << 16) | ((minor) << 8) | ((patch) & 0xFF))

include/numerics/tensor_tools.h

@@ -350,6 +350,51 @@ struct MakeBaseNumber<
   typedef typename MakeBaseNumber<T>::type type;
 };
 
+template <typename T, typename Enable = void>
+struct TensorTraits
+{
+  static_assert(always_false<T>,
+                "Instantiating the generic template of TensorTraits. You must specialize "
+                "TensorTraits for your type.");
+  static constexpr unsigned char rank = 0;
+};
+
+template <typename T>
+struct TensorTraits<T, typename std::enable_if<ScalarTraits<T>::value>::type>
+{
+  static constexpr unsigned char rank = 0;
+};
+
+template <typename T>
+struct TensorTraits<TypeVector<T>>
+{
+  static constexpr unsigned char rank = 1;
+};
+
+template <typename T>
+struct TensorTraits<VectorValue<T>>
+{
+  static constexpr unsigned char rank = 1;
+};
+
+template <typename T>
+struct TensorTraits<TypeTensor<T>>
+{
+  static constexpr unsigned char rank = 2;
+};
+
+template <typename T>
+struct TensorTraits<TensorValue<T>>
+{
+  static constexpr unsigned char rank = 2;
+};
+
+template <typename T, unsigned int N>
+struct TensorTraits<TypeNTensor<N, T>>
+{
+  static constexpr unsigned char rank = static_cast<unsigned char>(N);
+};
+
 }//namespace TensorTools
 
 }//namespace libMesh

tests/Makefile.am

@@ -99,6 +99,7 @@ unit_tests_sources = \
   numerics/diagonal_matrix_test.C \
   numerics/lumped_mass_matrix_test.C \
   numerics/eigen_sparse_matrix_test.C \
+  numerics/tensor_traits_test.C \
   parallel/message_tag.C \
   parallel/packed_range_test.C \
   parallel/parallel_sort_test.C \