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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: MI ammunition : linked lists
Date: 06 Nov 2003 21:03:59 +0000
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"Jean-Pierre Rosen" <rosen@adalog.fr> writes:

> "amado.alves" <amado.alves@netcabo.pt> a �crit dans le message de news:mailman.293.1068136383.25614.comp.lang.ada@ada-france.org...
> >A very common programming task where multiple inheritance (MI) would be
> >handy: implementation of doubly linked lists.
> [snip]
> 
> >  type Middle_Node is new First_Node with Last_Node;
> I would take this as a typical example of abuse of MI.  Inheritance
> should reflect an "is a" relationship. Do you fill comfortable
> stating that a middle node is a first node and a last node at the
> same time?

I think the names are wrong: Followed_Node and Preceded_Node might be
better. In which case a Middle_Node would indeed be both.

I think the problem occurs when adding at the front or back of the
list -- what was a Preceded_Node (at the end) now has to be replaced
by a Middle_Node, which means that the next-to-last node has to have
its Followed_By pointer changed to access the new next-to-last node
.. grim .. similar problems on deletion .. really not worth the
aggravation!

> My advice would be: use MI (and SI as well) IF AND ONLY IF it makes
> things simpler.  Don't bother if people tell you that you are not
> "purely object oriented" ;-)

Yes!

-- 
Simon Wright                               100% Ada, no bugs.