[fvGeometry] Make range generators free functions / friend functions

We iterate over all scvs of a fvElementGeometry like this
for (const auto& scv : scvs(fvGeometry))
This is closer to the way we speak "For each scv in all scvs of the fvElementGeometry do..."
and analogously to how we iterate over elements of a gridView.

dumux/porousmediumflow/3p3c/implicit/model.hh

@@ -164,7 +164,7 @@ public:
                 this->curVolVars_().bindElement(element);
 
                 const auto& fvGeometry = this->fvGeometries(element);
-                for (const auto& scv : fvGeometry.scvs())
+                for (const auto& scv : scvs(fvGeometry))
                 {
                     auto dofIdxGlobal = scv.dofIndex();
                     if (priVarSwitch_().wasSwitched(dofIdxGlobal))
@@ -306,7 +306,7 @@ public:
             this->curVolVars_().bindElement(element);
 
             const auto& fvGeometry = this->fvGeometries(element);
-            for (const auto& scv : fvGeometry.scvs())
+            for (const auto& scv : scvs(fvGeometry))
             {
                 const auto& volVars = this->curVolVars(scv);
                 int dofIdxGlobal = scv.dofIndex();

dumux/porousmediumflow/compositional/primaryvariableswitch.hh

@@ -61,7 +61,7 @@ public:
             problem.model().fvGeometries_().bindElement(element);
 
             const auto& fvGeometry = problem.model().fvGeometries(element);
-            for (auto&& scv : fvGeometry.scvs())
+            for (const auto& scv : scvs(fvGeometry))
             {
                 auto dofIdxGlobal = scv.dofIndex();
                 phasePresence_[dofIdxGlobal] = problem.initialPhasePresence(scv);
@@ -128,7 +128,7 @@ public:
             volVarsVector.bindElement(element);
 
             const auto& fvGeometry = problem.model().fvGeometries(element);
-            for (const auto& scv : fvGeometry.scvs())
+            for (const auto& scv : scvs(fvGeometry))
             {
                 auto dofIdxGlobal = scv.dofIndex();
                 if (!visited_[dofIdxGlobal])

test/implicit/test_fvelementgeometry.cc

@@ -114,22 +114,22 @@ int main (int argc, char *argv[]) try
         std::cout << std::endl << "Checking fvGeometry of element " << eIdx << std::endl;
         auto fvGeometry = fvGeometries.fvGeometry(eIdx);
 
-        auto range = fvGeometry.scvs();
+        auto range = scvs(fvGeometry);
         NoopFunctor<SubControlVolume> op;
         if(0 != testForwardIterator(range.begin(), range.end(), op))
             DUNE_THROW(Dune::Exception, "Iterator does not fulfill the forward iterator concept");
 
-        for (auto&& scv : fvGeometry.scvs())
+        for (const auto& scv : scvs(fvGeometry))
         {
             std::cout << "-- scv center at: " << scv.center() << std::endl;
         }
 
-        auto range2 = fvGeometry.scvfs();
+        auto range2 = scvfs(fvGeometry);
         NoopFunctor<SubControlVolumeFace> op2;
         if(0 != testForwardIterator(range2.begin(), range2.end(), op2))
             DUNE_THROW(Dune::Exception, "Iterator does not fulfill the forward iterator concept");
 
-        for (auto&& scvf : fvGeometry.scvfs())
+        for (const auto& scvf : scvfs(fvGeometry))
         {
             std::cout << "-- scvf center at: " << scvf.center();
             if (scvf.boundary()) std::cout << " (on boundary).";

test/porousmediumflow/3p3c/implicit/infiltrationproblem.hh

@@ -347,7 +347,7 @@ public:
             this->model().fvGeometries_().bindElement(element);
             const auto& fvGeometry = this->model().fvGeometries(element);
 
-            for (const auto& scv : fvGeometry.scvs())
+            for (const auto& scv : scvs(fvGeometry))
             {
                 auto dofIdxGlobal = scv.dofIndex();
                 (*Kxx)[dofIdxGlobal] = this->spatialParams().intrinsicPermeability(scv);