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From: Dmitry A. Kazakov <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Imitation is the sincerest form of flattery
Date: Wed, 26 Mar 2003 14:35:52 +0100
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Date: 2003-03-26T14:35:52+01:00
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On 25 Mar 2003 23:48:40 -0800, amir@iae.nsk.su (Amir Yantimirov)
wrote:

>Exactly. Only in my C++ head it is sounds as "address of particular
>interface dispatch routine" instead of "tag". :)

Which is not the same. Tag is not an address of a routine. In C++ it
might be a pointer to a list of such addresses. But even this becomes
wrong in case of multiple dispatch. That's when the dispatch table of
a routine is mutli-dimensional and tags have to be mapped to the
indices of the table.

The point is that because Ada differentiates X / access X and X'Class
/ access X'Class types it is possible (*) to strip the tag away from a
specific object or pointer. Thus to make a type "tagged" would cost
absolutely nothing as long as no class-wide objects / pointers and
routines are used.

(*) If redispatch would be disallowed someday.

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