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From: Cyrille <comar@eu.adacore.com>
Newsgroups: comp.lang.ada
Subject: Re: Preventing type extensions
Date: Tue, 21 Sep 2010 10:37:09 -0700 (PDT)
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On Sep 21, 4:50=A0pm, "(see below)" <yaldni...@blueyonder.co.uk> wrote:
> > all OO languages I'm aware of, have the notion of classwide types...
> > They just don't make the distinction between a type on its own and a
> > type with its derived types. If you think about it, it is a peculiar
> > distinction at the "design" level. A horse is an animal... When I deal
> > with animals, I must be ready to accept that maybe the animal I'm
> > dealing with may be a horse, or may be something else. It's peculiar
> > to expect it to be the pure notion of "animal" and nothing else...
>
> What is peculiar about abstraction?

Abstraction is a good thing. Differentiating between Animals and
Animals'Class doesn't particularly help abstraction, as far as I am
concerned. This differentiation was a neat way to introduce OO into an
existing language such as Ada 83, I don't think there is more to it
than that.