From: Karl von Laudermann <doodpants@...>
Date: 2008-11-05T23:29:10+09:00
Subject: Re: Ruby's take on S.O.L.I.D.

On Nov 4, 5:45 pm, Mike Lopke <reglo...@cableone.net> wrote:
> For example, the typical Liskov Substitution example you see in Java has
> the case where you have a Rectangle class and a derived Square class.
> The Rectangle has an independent width and height. They have to be the
> same for the Square.

One guiding principle when designing a class heirarchy is that the
class with fewer data members should be the superclass, and the class
with more data members should be the subclass. This sometimes leads to
cases which are counterintuitive with respect to the way we think of
things in real life. For example, Rectangle should be a subclass of
Square, not the other way around. This is because the Square class
only needs one dimension member variable, e.g. "width", and the
Rectangle subclass needs to add a second one, e.g. "height".