Re: SIGada Conference

[Hyman Rosen <hyrosen@mail.com>]

Jean-Pierre Rosen wrote:
> "Hyman Rosen" <hyrosen@mail.com> a �crit
>>I expect this is just the usual "simulate MI with access discriminants"
>>bit that always comes up here. I think it can do everything except support
>>cross-casting.
> 
> It can. See my paper at http://www.adalog.fr/publicat/ada-interfaces.pdf

Does this mean that you think it can support cross-casting,
or do you agree that it cannot? That is, in Java, I may have
two interfaces:
     interface IF_1 { }    interface IF_2 { }
and given an object of type IF_1, I may try to see if it is
also of type IF_2:
     boolean is_both(IF_1 o) { return o instanceof IF_2; }
and if it is, I can cross-cast:
     IF_2 as_IF_2(IF_1 o) { return is_both(o) ? (IF_2)o : null; }

Note that I can do this without any knowledge at all of the
existence of one or more parent types which implement both
interfaces. I don't think this can be done with the inner class/
access discriminant approach.