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From: "Mark A. Biggar" <mark@biggar.org>
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Subject: Re: C bug of the day
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Date: 2003-06-20T21:12:54+00:00
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Dmitry A. Kazakov wrote:

> 2. multiple inheritance
> 
> Missing 2. in Ada is clearly a design fault.  

Not really, just a realization at the time (92-93) that they couldn't
make too big a change in the language, if they wanted the implementors
to go with the changes to the standard.  MI was considered along with
the current SI model and it was determined that given all the extra
mechanisms needed to solve such problems as the method/field ambiguities
in the diamond inheritance example it was too big a change to the
language.  Note that the language already had most of what what was
needed for SI in derived types so all they had to add was support for
field extension when deriving and a protocol for run-time dispatch.
SI also has a very simple implementation model (the tag field is a
simple pointer to a vtable with constant offsets for method lookup).
But as MI needs to deal with multiple inherited vtables with much more
complicated implementation.