[DGD] Inheriting the same program twice

[Thomas Rice]

If A inherits B... And B inherits X... There shouldn't be any need for
A to inherit X, as it already can call functions defined in X by
inheriting B.

On 4/19/05, Petter Nyström <md1pette at mdstud.chalmers.se> wrote:
> I have run into a situation where it would make sense to have an object
> inherit a program twice, at different points in the inheritance tree.
> 
> With some ascii-graphic my inheritance tree would look like:
> 
>            A
>           / \
>          B   X
>         / \
>        X  ...
> 
> (Or in words: A inherits B and X, B inherits X.)
> 
> I am somehow led to believe this is very bad design, because as my code
> looks right now this shouldn't even compile. That is because I haven't
> defined any of the functions in X in A, so calls to these function in
> objects of type A should be ambiguos, but they are not and it does
> compile. This hints that maybe it doesn't matter if you inherit the same
> program multiple times in one object, it will still only have one data
> space for that program?
> 
> I would be happy if someone could tell me some truths on this subject. And
> perhaps also suggest good design alternatives to my problem here. It do
> makes sense for me to have objects of type A to have duplicated and
> separable data fields as defined by X.
> 
> Jimorie
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