Rely on RVO; Allows to construct just once object

dune/tectonic/globallaursennonlinearity.hh

@@ -34,11 +34,11 @@ class GlobalLaursenNonlinearity
 
     sigma_n [id + mu id] = sigma_n (1 + mu) id
   */
-  virtual void restriction(int i, OuterFunctionType &f) const {
+  OuterFunctionType restriction(int i) const {
     double coefficient = nodalIntegrals[i][0];
     coefficient *= normalStress[i];
     coefficient *= 1 + coefficientOfFriction[i];
-    f = OuterFunctionType(coefficient);
+    return OuterFunctionType(coefficient);
   }
 
 private:

dune/tectonic/globalnonlinearity.hh

@@ -11,7 +11,7 @@ template <int dim, class OuterFunctionType> class GlobalNonlinearity {
   /*
     Return a restriction of the outer function to the i'th node. If
   */
-  virtual void restriction(int i, OuterFunctionType &f) const = 0;
+  virtual OuterFunctionType restriction(int i) const = 0;
 };
 }
 #endif

dune/tectonic/myblockproblem.hh

@@ -114,8 +114,7 @@ class MyBlockProblem<MyConvexProblemTypeTEMPLATE>::IterateObject {
       }
       assert(localA != NULL);
 
-      FunctionType f;
-      problem.phi.restriction(m, f);
+      auto const f = problem.phi.restriction(m);
       Dune::LocalNonlinearity<block_size> const phi(f);
       Dune::SampleFunctional<block_size> localJ(*localA, localb, phi,
                                                 ignore_component);