[Dune] Storing entity iterators

[Agnese, Marco]

Hi Steffen, hi Christian Engwer and hi Oliver,
thank you for your answers. I wasn't aware that entity iterators were expensive. 
Therefore storing a copy of the entities (or the entity seed) is the correct solution. 
Good news since that was the solution I had implemented :)

Another very quick question. 

Let's suppose that I have a GeometryGrid and I store a copy of an entity. 
After that, I move the vertices of my grid (therefore I change the values of the discrete function defined on the host grid which defines my wrapped grid). 
The entity copy extracted before is consistent with the updated GeometryGrid or is consistent with the old one? 
More precisely, if I extract a vertex of the entity copy, the global coordinate will have the same value of the old grid or of the new grid?
Does it change the behaviour, if I store the entity seed instead of the entity copy?

Thank you very much,
cheers,
Marco.