dolfin team mailing list archive

[Dag Lindbo <dag@xxxxxxxxxx>]

Thanks Martin! It is much clearer now. My main concern here is as a 
"user", since a release is forthcoming. I only wish to clarify things 
here for the benefit of (myself and) other users. Comments below.

Martin Sandve Alnæs wrote:
> 2008/4/15, Dag Lindbo <dag@xxxxxxxxxx>:
> > Hello!
> >
> >  A lot has happened on the Vector/Function/<backend>Vector interface the
> >  last weeks. For clarity, I would like to have a little "summing up"
> >  thread. That is, I  think it would be beneficial to explicitly show how
> >  the new interface is intended to be used. Sounds good? Here are some
> >  situations, to which I propose solutions. Please correct if these are
> >  not in line with the intended interface, or if there are better ones.
> >
> >  How to:
> >  *) Get reference to Vector from a (discrete) Function u
> >  Vector& v = dynamic_cast<Vector&>(u.vector());
>
> Why would you want that?
> All dolfin library code will now use GenericVector references.
> This way it will also work with f.ex. uBlasVector objects directly.

I understand that Generic* is used for all internal DOLFIN code.

It is still not clear how "application code", i.e. an actual solver for 
a user, is supposed to do this. Is GenericVector from now on part of the 
public interface of DOLFIN? (sorry if I'm repeating this question)

> So:
>
> GenericVector& v = u.vector();
>
>
> >  *) Get reference to uBlasVector from Vector v:
> >  uBlasVector& uv = dynamic_cast<uBlasVector&>(*v.instance());
>
> uBlasVector& uv = v.down_cast<uBlasVector>();
>
>
> >  *) Get reference to PETScVector from Vector:
> >  ???
>
> PETScVector& pv = v.down_cast<PETScVector>();
>
>
> >  *) Get reference to uBlasVector from (discrete) Function u
> >  uBlasVector& uv = dynamic_cast<uBlasVector&>(*u.vector().instance());
>
> uBlasVector& uv = u.vector().down_cast<uBlasVector>();
>
>
> >  *) Get reference to PETScVector from (discrete) Function u
> >  ???
>
> PETScVector& uv = u.vector().down_cast<PETScVector>();
>
>
> >  Please add more situations and suggestions. Thanks!
>
> In general, this works with v being any subclass of GenericVector
> including Vector:
>
> Foo & fv = v.down_cast<Foo>();
>
> It will trigger a dolfin error on failure.
> You can check the backend in use like:
>
> bool b = v.has_type<Foo>();
>
> with Foo being uBlasVector, PETScVector, etc.
>
> The point is that v.down_cast<MyVec> and v.has_type<MyVec> works with
> v being an instance of MyVec or an instance of Vector with MyVec as
> the actual backend.

Very nice!

> --
> Martin