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Date: Thu, 01 Aug 2002 12:30:50 -0400
From: Hyman Rosen <hyrosen@mail.com>
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Subject: Re: Dispatching and generics - language lawyer question
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Date: 2002-08-01T12:30:50-04:00
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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>.

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.