add static assert in mpifuturetest

dune/common/parallel/test/mpifuturetest.cc

@@ -6,14 +6,17 @@
 #include <dune/common/dynvector.hh>
 
 namespace Dune {
-  template<>
-  struct MPIData<const int&>{
+  template<class Dummy>
+  struct MPIData<const int&, Dummy>
+  {
+    static_assert(Dune::AlwaysFalse<Dummy>::value, "MPIData of reference type should not be used!");
     // MPIData of reference type should not be used!
     // This struct should never be used it just
     // exists to generate a compiler error
   };
 }
 
+
 int main(int argc, char** argv){
   auto& mpihelper = Dune::MPIHelper::instance(argc, argv);