[Dune] Returning Geometries As Objects (again)

[Christian Engwer]

Hi Martin,

> >[1] Actually, the idea of having Geometry objects that look like value
> >objects but behave like references scares me quite a bit. Before,
> >we had object lifetime issues with geometries, because they where
> >just references. But at least you could see there was trouble because
> >the relevant methods returned references. If the methods now return
> >objects without the little '&', but the lifetime behavior stays the
> >same, then I foresee major debugging trouble and user frustration.

I must agree, this is the one point that bothers me most. As you said,
it is for transition, and I think it might be valuable for the grid
implementers to update their code. Still I'd like to have the
"reference"-feature removed before the next release, in order to avoid
problems in the user codes. When discussing the object-vs-reference
issues we had two problems in mind. For me the life-time problem was a
major point here, so I would not like to drop it in the end.

Btw., thank you for this great affort.

Cheers
Christian