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From: "Grein, Christoph" <christoph.grein@eurocopter.com>
Newsgroups: comp.lang.ada
Subject: Re: Invoking abstract subprograms in Ada95
Date: Wed, 24 Apr 2002 09:32:42 +0200 (MET DST)
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Date: 2002-04-24T09:32:42+02:00

> "Grein, Christoph" <christoph.grein@eurocopter.com> wrote in message 
news:<mailman.1019483282.562.comp.lang.ada@ada.eu.org>...
> 
> > Class-wide operations cannot be abstract, they also cannot be overrridden.
> > 
> > OK, they can be abstract, this is why your code compiles, but abstractness 
here 
> > has a devastating meaning: There can never be such an operation!
> 
> 
> Aha. Now I see the error of my ways.
> 
> > 
> > 
> > > end abstract_bit;
> > > 
> > > --
> > > package body abstract_bit is
> > > 
> > > procedure generalOperation( this : in out A'class ) is
> > > begin
> > >     specificOperation( this => this );
> > 
> > You said it was abstract, so does not exist! Therefore you cannot call it 
here.
> 
> Weeell in my mind, for generalOperation to be invoked, 'A' must have
> been extended sufficiently to be non abstract, and therefore an
> implementation of specificOperation *must* exist ;)

No, it can't exist because you defined it class-wide and abstract. It can only 
exist if you defined it class-specific and abstract. This is what my previous  
code example showed.