On Thu, Oct 08, 2009 at 01:22:23PM +0200, Johan Hake wrote: > On Tuesday 29 September 2009 15:15:12 Anders Logg wrote: > > On Tue, Sep 29, 2009 at 03:07:33PM +0200, Johan Hake wrote: > > > On Tuesday 29 September 2009 14:06:20 Garth N. Wells wrote: > > > > Anders Logg wrote: > > > > > On Tue, Sep 29, 2009 at 01:01:35PM +0100, Garth N. Wells wrote: > > > > >> Anders Logg wrote: > > > > >>> On Tue, Sep 29, 2009 at 12:42:54PM +0100, Garth N. Wells wrote: > > > > >>>> Anders Logg wrote: > > > > >>>>> On Tue, Sep 29, 2009 at 07:39:01AM +0100, Garth N. Wells wrote: > > > > >>>>>> Is there a reason why the MeshFunction.get(..) functions return > > > > >>>>>> by value rather then reference, e.g. it is currently > > > > >>>>>> > > > > >>>>>> inline T get(const MeshEntity& entity) const > > > > >>>>>> > > > > >>>>>> rather than > > > > >>>>>> > > > > >>>>>> inline T& get(const MeshEntity& entity) const > > > > >>>>>> > > > > >>>>>> Garth > > > > >>>>> > > > > >>>>> Yes, we have a set() function for setting the values. > > > > >>>> > > > > >>>> I know, but I would like to get a reference rather than copying > > > > >>>> data > > > > >>>> > > > > >>>> unsigned int index = 3; > > > > >>>> const std::vector<double>& vec = mesh_function.get(index) > > > > >>>> > > > > >>>> I can do this when I have the MeshEntitiy, but not when using the > > > > >>>> index. > > > > >>> > > > > >>> Does it work if you do > > > > >>> > > > > >>> &vec[0] = mesh_function.values(); > > > > >> > > > > >> Probably, bit it's not what I want. I have a std::vector attached to > > > > >> mesh entities (MeshFunction<std::vector<double> >). I want a > > > > >> reference to the std::vector attached to a particular entity > > > > >> > > > > >> std::vector<double> vec& = mesh_function(my_entity); > > > > >> > > > > >> is fine, but > > > > >> > > > > >> std::vector<double> vec& = mesh_function.get(my_index); > > > > >> > > > > >> is not. > > > > > > > > > > What if you just add operator[] for uint? > > > > > > > > > >> Back to my question: Is there a reason why MeshFunction::get returns > > > > >> by value and not by reference? > > > > > > > > > > There might be a reason. I think we introduced get/set for use in the > > > > > Python interface. Perhaps Johan remembers? > > > > > > Well, this was before my time ;) > > > > > > But I see that get is used to overload the __call__ method in Python. I > > > am quite sure this can be done in a nicer way. We probably had > > > difficulties with extending the MeshFunctions as these are templated > > > classes. We know how to do this now. > > > > > > I am not sure why we return by value, but it might have something to do > > > with memory management in Python. However these things could be handled > > > in the wrapper layer anyway. > > > > > > I suggest we define the C++ interface as we want it to be, then I am > > > quite sure I can mimic this in Python. (starting to get bald I think ;)) > > > > > > So whats the logic here. Should > > > > > > &T operator() > > > > > > be used when we have the entity, and maybe > > > > > > &T operator[] > > > > > > when we have the index, or should one of the operators be used for both > > > cases? > > > > I think it would be safe to overload operator[]. > > Do we still want to make this transition? I have started it but it requires > quite a lot of changes... > > Johan
I guess it would be nice to have. Why does it require many changes? It's just adding a new function (at least in C++). -- Anders
signature.asc
Description: Digital signature
_______________________________________________ DOLFIN-dev mailing list DOLFIN-dev@fenics.org http://www.fenics.org/mailman/listinfo/dolfin-dev
