Re: SIGada Conference

["Jean-Pierre Rosen" <rosen@adalog.fr>]

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"Hyman Rosen" <hyrosen@mail.com> a �crit dans le message de news:1071687303.254780@master.nyc.kbcfp.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.
>
What I meant is that if class A implements interface IF, and you get an object as an IF, you can get a view of it as an A. I didn't
consider the case you mention - presumably because I never met a need for it!

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           J-P. Rosen (rosen@adalog.fr)
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