From 071f982eddcacb5d3efcb8fa7d0b1491273e7625 Mon Sep 17 00:00:00 2001
From: Denis Davydov <davydden@gmail.com>
Date: Thu, 21 Feb 2019 23:20:50 +0100
Subject: [PATCH] add internal::has_partitioners_are_compatible<>

---
 include/deal.II/matrix_free/fe_evaluation.h   | 21 +++++++++++++++++++
 .../matrix_free/fe_evaluation_type_traits.cc  | 11 ++++++++++
 ...tion_type_traits.with_trilinos=true.output |  3 +++
 3 files changed, 35 insertions(+)

diff --git a/include/deal.II/matrix_free/fe_evaluation.h b/include/deal.II/matrix_free/fe_evaluation.h
index dc97327d07..c7c2d8b890 100644
--- a/include/deal.II/matrix_free/fe_evaluation.h
+++ b/include/deal.II/matrix_free/fe_evaluation.h
@@ -3438,6 +3438,27 @@ namespace internal
   };
 
 
+  // same as above to check
+  // bool T::partitioners_are_compatible(const Utilities::MPI::Partitioner &)
+  // const
+  template <typename T>
+  struct has_partitioners_are_compatible
+  {
+  private:
+    static void
+    detect(...);
+
+    template <typename U>
+    static decltype(std::declval<U const>().partitioners_are_compatible(
+      std::declval<Utilities::MPI::Partitioner>()))
+    detect(const U &);
+
+  public:
+    static constexpr bool value =
+      std::is_same<bool, decltype(detect(std::declval<T>()))>::value;
+  };
+
+
   // access to generic vectors that have operator ().
   // FIXME: this is wrong for Trilinos/Petsc MPI vectors
   template <typename VectorType,
diff --git a/tests/matrix_free/fe_evaluation_type_traits.cc b/tests/matrix_free/fe_evaluation_type_traits.cc
index 458a625e8a..12ab08476b 100644
--- a/tests/matrix_free/fe_evaluation_type_traits.cc
+++ b/tests/matrix_free/fe_evaluation_type_traits.cc
@@ -118,5 +118,16 @@ main()
   internal::vector_access(dummy2, 0);
 
 
+  // now check has_partitioners_are_compatible:
+  deallog << "has_partitioners_are_compatible:" << std::endl
+          << "LinearAlgebra::distributed::Vector = "
+          << internal::has_partitioners_are_compatible<
+               LinearAlgebra::distributed::Vector<double>>::value
+          << std::endl
+          << "TrilinosWrappers::MPI::Vector = "
+          << internal::has_partitioners_are_compatible<
+               TrilinosWrappers::MPI::Vector>::value
+          << std::endl;
+
   deallog << "OK" << std::endl;
 }
diff --git a/tests/matrix_free/fe_evaluation_type_traits.with_trilinos=true.output b/tests/matrix_free/fe_evaluation_type_traits.with_trilinos=true.output
index 78f0765434..4e82d52202 100644
--- a/tests/matrix_free/fe_evaluation_type_traits.with_trilinos=true.output
+++ b/tests/matrix_free/fe_evaluation_type_traits.with_trilinos=true.output
@@ -7,4 +7,7 @@ DEAL::Dummy2 = 0
 DEAL::internal::vector_access:
 DEAL::Dummy::local_element()
 DEAL::Dummy2::operator()
+DEAL::has_partitioners_are_compatible:
+DEAL::LinearAlgebra::distributed::Vector = 1
+DEAL::TrilinosWrappers::MPI::Vector = 0
 DEAL::OK
-- 
2.39.5