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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Subject: Re: Preventing type extensions
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Date: Tue, 21 Sep 2010 16:19:39 +0200
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Date: 2010-09-21T16:19:39+02:00
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On Tue, 21 Sep 2010 06:57:36 -0700 (PDT), Cyrille wrote:

> On Sep 13, 11:13�pm, "J-P. Rosen" <ro...@adalog.fr> wrote:
> 
>> These arguments make sense for languages without the notion of
>> class-wide types.
> 
> 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.

It is a distinction between a member and a set where it belongs to. These
are not equivalent. Furthermore a type may be member of more than one
classes (sets of types). Also an operation may be primitive in more than
one class (AKA multiple dispatch). In this context it is difficult to see
how the model of re-dispatching primitive operations could be made
feasible.

> A horse is an animal...

But animal is not necessary a horse.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de