From 46446db7262b34e2c26e59fc5b66345903cc62bd Mon Sep 17 00:00:00 2001
From: Denis Davydov <davydden@gmail.com>
Date: Tue, 26 Feb 2019 06:34:05 +0100
Subject: [PATCH] fix internal::has_begin type trait used in FEEvaluation

---
 include/deal.II/matrix_free/fe_evaluation.h                    | 3 +--
 tests/matrix_free/fe_evaluation_type_traits.cc                 | 3 ++-
 .../fe_evaluation_type_traits.with_trilinos=true.output        | 1 +
 3 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/include/deal.II/matrix_free/fe_evaluation.h b/include/deal.II/matrix_free/fe_evaluation.h
index 20b8249e03..77e6975cff 100644
--- a/include/deal.II/matrix_free/fe_evaluation.h
+++ b/include/deal.II/matrix_free/fe_evaluation.h
@@ -3466,8 +3466,7 @@ namespace internal
 
   public:
     static constexpr bool value =
-      std::is_same<typename T::const_iterator,
-                   decltype(detect(std::declval<T>()))>::value;
+      !std::is_same<void, decltype(detect(std::declval<T>()))>::value;
   };
 
 
diff --git a/tests/matrix_free/fe_evaluation_type_traits.cc b/tests/matrix_free/fe_evaluation_type_traits.cc
index 762da8b50d..ffa6552698 100644
--- a/tests/matrix_free/fe_evaluation_type_traits.cc
+++ b/tests/matrix_free/fe_evaluation_type_traits.cc
@@ -142,7 +142,8 @@ main()
     << std::endl
     << "TrilinosWrappers::MPI::Vector = "
     << internal::has_begin<TrilinosWrappers::MPI::Vector>::value << std::endl
-    << "Vector = " << internal::has_begin<Vector<double>>::value << std::endl;
+    << "Vector = " << internal::has_begin<Vector<double>>::value << std::endl
+    << "Dummy = " << internal::has_begin<Dummy<double>>::value << std::endl;
   // check is_vectorizable:
   deallog
     << "is_vectorizable:" << 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 801cf4191e..b7e821fc99 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
@@ -16,6 +16,7 @@ DEAL::has_begin:
 DEAL::LinearAlgebra::distributed::Vector = 1
 DEAL::TrilinosWrappers::MPI::Vector = 1
 DEAL::Vector = 1
+DEAL::Dummy = 0
 DEAL::is_vectorizable:
 DEAL::LinearAlgebra::distributed::Vector<double> && double = 1
 DEAL::LinearAlgebra::distributed::Vector<double> && float = 0
-- 
2.39.5