Re: MI ammunition : linked lists

["Jean-Pierre Rosen" <rosen@adalog.fr>]

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"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?

>But, semantically, MI would allow conversions between Middle_Node and any the other two extended types. >Whether this would be
useful for linked lists remains to be ascertained. I confess I have not implemented them this >way yet.
So you trade checking a null value for checking a node belonging to a certain class, with a number of extra conversions required....

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" ;-)

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           J-P. Rosen (rosen@adalog.fr)
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