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From: Dmitry A.Kazakov <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Dispatching and generics - language lawyer question
Date: Sat, 3 Aug 2002 01:42:02 +0200
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Date: 2002-08-03T01:42:02+02:00
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Hyman Rosen wrote:

> Dmitry A.Kazakov wrote:
>> I think that (1) would cause many problems with MI. When tag is a part of
>> the value and then view conversions are problematic.
>> There is also redispatch which is IMO incompatible with (1). I think
>> redispatch must be removed, because when object identification is really
>> necessary (to redispatch) one could use a solution similar to J.-P. Rosen
>> trick.
> 
> C++ uses (1), storing multiple "tags" (actually, virtual
> table pointers) in the object if necessary, and supports
> redispatch just fine. The scheme used by the new version
> of g++ is described at
> <http://www.codesourcery.com/cxx-abi/abi.html>.

So in C++ int will never be a class, worse to C++.
 
> I doubt that the language designers, assuming they do add
> MI to Ada, would be so silly as to deliberately choose to
> implement it in a way that could never be compatible with
> C++ object layout.

I do not think that to repeat others faults is a good idea. As long as we 
have no C++ operating system APIs (shudder), I doubt that it is worth 
effors to keep objects Ada and C++ compatible. To communicate with C++ one 
could declare a simple record type with fields reserved for places where 
vtptrs are.

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