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From: Dmitry A. Kazakov <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Extension of non-limited type needs limited component
Date: Fri, 15 Nov 2002 15:34:49 +0100
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Date: 2002-11-15T15:34:49+01:00
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On Fri, 15 Nov 2002 14:29:31 +0100, "Jean-Pierre Rosen"
<rosen@adalog.fr> wrote:

>"Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de> a �crit dans le message
>news:
>> Both Ada and SmallTalk [AFAIK] do not crash when such thing happens.
>> But this is not the problem. The problem is that though one could wish
>> to detect all such and similar cases at compile time, one cannot. This
>> does not mean that we should drop compile-time checks. [To put it
>> clear, Ada is right, SmallTalk is wrong! (:-))] It only means that the
>> argument, "this is not allowed, because it cannot be fully checked at
>> compile time" is wrong. Alas, there are many damn useful things
>> uncheckable at compile time.
>
>... with tagged types.
>
>The benefit, and drawback, of tagged types is that they allow dynamic
>typing, therefore requiring (isn't it surprising) dynamic checking. More
>flexibility, less security. If you want full compile-time checking, don't
>use tagged types.

You could also use a less restrictive "..., don't use class-wide
objects with tags unknown at compile-time."

>At least in Ada, you have a choice!

Right.

---
Regards,
Dmitry Kazakov
www.dmitry-kazakov.de