From: Jim Freeze <jim@...>
Date: 2002-12-15T00:27:58+09:00
Subject: Re: Inheritance Question

On Saturday, 14 December 2002 at 22:00:53 +0900, ts wrote:
> >>>>> "J" == Jim Freeze <jim@freeze.org> writes:
> 
> J> Don't you mean that this is how Array was implemented, not what
> 
>  Vect and Matrix are implemented via Array. It can be strange if Vect do
>  something and Array do another thing.
 
 cat v.rb
require 'matrix'

v1 = Vector[1]
v2 = Vector[2]
p ((v1+v2).class)

 ruby v.rb
 Vector

Here, Vector extends array and returns a Vector and NOT Array when
adding two Vectors. I don't see why an extension of Matrix should not
return the super class. Same for Array.

> J> The language doesn't force one to always return the base class.
> 
>  I know this but there are other classes in ruby which do like Array (don't
>  remember actually but this seems to be a voluntary choice)
 
 I agree that in general, it would be difficult to ensure that every 
 library returns self for chainable methods. But, I do think it is a
 good practice, especially if you expect your class to used as a base
 class.
 
 For the case of Matrix, it makes it impracticle to be used as a base
 class. To extend the class, I would have to do it directly and hope
 that I don't cause any problems. But when I am writing numerical code,
 I usually have accuracy as my primary goal, so I am unlikely to extend
 the class directly because it may have side effects.
 

-- 
Jim Freeze