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From: Ludovic Brenta <ludovic@ludovic-brenta.org>
Newsgroups: comp.lang.ada
Subject: Re: Ada Interfaces and the Liskov Substitution Principle
References: <Pine.LNX.4.64.0705232101220.20072@th.informatik.uni-mannheim.de>
Date: Wed, 23 May 2007 22:32:49 +0200
Message-ID: <871wh7i8lq.fsf@ludovic-brenta.org>
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Date: 2007-05-23T22:32:49+02:00
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Stefan Lucks <lucks@th.informatik.uni-mannheim.de> writes:
> package Parents is
>    type Parent is Interface;
>
>    -- primitive operation
>   procedure Do_Something(Self: in out Parent) is abstract;
>
>    -- class-wide operations
>    procedure Do_Nothing(From: in Parent'Class;
>                         To:  out Parent'Class);
>    procedure Convert(From: in Parent'Class;
>                      To:  out Parent'Class);
> end Parents;

> with Parents, Ada.Finalization;
>
> package Stepchild is
>
>    type Object is
>      new Ada.Finalization.Limited_Controlled
>      and Parents.Parent
>      with private;
>
>    procedure Do_Something (Self: in out Object);
>
> private
>
>    ... doesn't really matter ...
>
> end Stepchild;

> 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."

Since GNAT is currently the only compiler with Ada 2007 features, I
presume it must be a bug in GNAT.  What version are you using?

-- 
Ludovic Brenta.