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? Johan > OK, that's what I want to know. > > Garth > > > -- > > Anders > > > > > > ------------------------------------------------------------------------ > > > > _______________________________________________ > > DOLFIN-dev mailing list > > DOLFIN-dev@fenics.org > > http://www.fenics.org/mailman/listinfo/dolfin-dev > > _______________________________________________ > DOLFIN-dev mailing list > DOLFIN-dev@fenics.org > http://www.fenics.org/mailman/listinfo/dolfin-dev > _______________________________________________ DOLFIN-dev mailing list DOLFIN-dev@fenics.org http://www.fenics.org/mailman/listinfo/dolfin-dev