dolfin team mailing list archive

["Johan Hoffman" <jhoffman@xxxxxxxxxx>]

> 2008/4/15, 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)
>
>
> Actually, I think you've pointed out a user interface problem here.
> We can in general go from Vector to backend-type, but not the other way
> around.
>
> You _can_ do this:
>     Vector& v = dynamic_cast<Vector&>(u.vector());
> _if_ your code has been using Vector consistently.
> It will throw a std::bad_cast exception otherwise.
>
> But that will limit that part of your code to built-in dolfin backends,
> which
> is one of the things we're trying to avoid by using GenericVector&
> everywhere.
>
> On the other hand, if you use
>     GenericVector& v = u.vector();
> this does, as you say, make GenericVector enter user code alongside
> Vector,
> which was something Anders didn't want to begin with (if I remember
> correctly?).
>
> From Python, this is not an issue.

In C++ user code, I guess that you can use your own typedef for the Generic*

/Johan

> --
> Martin
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