Use more curly brace initialization in return statements.

source/geometry_model/interface.cc

@@ -52,7 +52,7 @@ namespace aspect
     Interface<dim>::get_periodic_boundary_pairs() const
     {
       // return an empty set in the base class
-      return std::set<std::pair<std::pair<types::boundary_id, types::boundary_id>, unsigned int>>();
+      return {};
     }
 
 
@@ -85,7 +85,7 @@ namespace aspect
       Assert (false,
               ExcMessage ("The cartesian_to_natural_coordinates function has "
                           "not been implemented in this geometry model."));
-      return std::array<double,dim>();
+      return {};
     }
 
 

source/particle/generator/interface.cc

@@ -105,7 +105,7 @@ namespace aspect
         return std::make_pair(cell,particle);
 
         // Avoid warnings about missing return
-        return std::pair<Particles::internal::LevelInd,Particle<dim>>();
+        return {};
       }
 
 

source/particle/property/interface.cc

@@ -403,7 +403,7 @@ namespace aspect
                                               const typename parallel::distributed::Triangulation<dim>::active_cell_iterator &cell) const
       {
         if (property_information.n_components() == 0)
-          return std::vector<double>();
+          return {};
 
         std::vector<double> particle_properties;
         particle_properties.reserve(property_information.n_components());

source/simulator/assemblers/interface.cc

@@ -555,7 +555,7 @@ namespace aspect
                              "then this function should be implemented. "
                              "If this is an assembler that does not have to compute a residual, it should not be called."));
 
-      return std::vector<double>();
+      return {};
     }