[Dune] Returning Geometries As Objects

[Christian Engwer]

I fully support Carstens view.

> I also consider the branch tested well enough to be merged.
> However, the crucial point is (b)/(c):
> 
> I'd not like to have objects that behave like references
> and I do totally agree with Oliver on the potential bad
> consequences.
> 
> On the other hand I'm afraid that postponing the merge
> until after a discussion on the next meeting would mean
> a significant amount of extra work for Martin who has
> already invested much time to implement this.
> 
> @(b): I propose to decide on (c) now
> @(c): I'd expect geometry objects to have the same
>       life time as EntityPointers now, i.e., until
>       the next grid modification (*)
> If we decide to have (*) I'd furthermore like to...
> 
> @(a): ... do the branch now to avoid extra work.
> @(d): ... implement (*) before the branch even if one
>       would have the adapt the application code to get
>       the same performance (this has to be done anyway).
>       If there are serious concerns about this we
>       might think of making this adjustable via
>       some macro switch.
> @(e): ... not do have a release before the branch in
>       view of the extra work for testing things we
>       already consider outdated.

To comment on Andreas question, I would like to discuss this
particular issue seperate from indexsets and intersections.

Cheers
Christian