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From: Anh Vo <anhvofrcaus@gmail.com>
Newsgroups: comp.lang.ada
Subject: Re: Ada Interfaces and the Liskov Substitution Principle
Date: 23 May 2007 17:56:44 -0700
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Date: 2007-05-23T17:56:44-07:00
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On May 23, 3:00 pm, "Randy Brukardt" <r...@rrsoftware.com> wrote:
> "Ludovic Brenta" <ludo...@ludovic-brenta.org> wrote in message
>
> news:871wh7i8lq.fsf@ludovic-brenta.org...
>
> > Stefan Lucks <l...@th.informatik.uni-mannheim.de> writes:
> ...
> > > What do you guys think about this?
>
> > I think the declaration of Stepchild.Object is illegal because ARM
> > 3.9.4(12/2) states: "A type derived from a nonlimited interface shall
> > be nonlimited."
>
> Right. The most general type of interface is a limited interface; every
> interface should be declared limited if possible. (We didn't make that the
> default solely because it would be inconsistent with the rest of the
> language.) And if it is not possible to declare the interface limited (as in
> the example), then all types that include it must be nonlimited. At least
> interfaces don't have the rather limiting rule that regular tagged types do,
> where the limitedness can't be changed at all.

Indeed, GNAT-GPL-2007 complains that "stepchild.ads:12:04: progenitor
interface "Parent" of limited type must be limited". In addition, if
the Object is changed Controlled type instead, there is no problem
with compilation.

AV