Python Design Patterns - composition vs. inheritance

[Matthieu Brucher]

>
> > >    Well, you would if you override the two set_* methods to set both
> > > height and width to the same value <G>
> >
> > But that breaks expectations: a user doesn't expect set_width() to
> affect
> > the height.
>
> I can't speak for everyone but I certainly expect setting the width of
> a Square to change it's height. In fact, that would probably be the
> reason I used a Square rather than a Rectangle in the first place.
>

You might expect this, but the algorithm that resizes a rectangle for some
reason does not expect this. That's why a Square IS NOT a Rectangle from an
IT point of view, even if it is from a mathematical one. I see this every
day in my code, and if a square were to be given instead of a recatngl, all
my code would break immediately.
One can see inheritance as a generalization, not the opposite.

Matthieu
-- 
French PhD student
Website : http://miles.developpez.com/
Blogs : http://matt.eifelle.com and http://blog.developpez.com/?blog=92
LinkedIn : http://www.linkedin.com/in/matthieubrucher
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