From: "T. Onoma" <transami@...>
Date: 2003-12-24T04:09:50+09:00
Subject: Re: Copying methods from one class to another

On Tuesday 23 December 2003 09:51 am, Ian Hobson wrote:
> This still does not answer the question of why? (At least for me), so
> I'm jumping in here are asking it again!
>
> When you can simply extend class A with any new method you need, why do
> you want to create a subclass and pretend it is the class you started
> with?

James' answer is correct. We have been discussing Aspect Oriented Programming 
for Ruby in-depth, the main feature of which is method wrapping (known as 
*advice* in AOP terms). Currently method wrapping is generally approached via 
method aliasing, but a better way comes from the realization that subclassing 
already entails method wrapping. All that is needed is a way to *annonymously 
subclass*.

  class A < A

is one way to to do this, but requires moving method definitions into the 
super class when they are subsequently defined. It is not a perfect solution, 
and was merely used in one possible test implementation.

That's a highly concise explination. If you are interested in this, 
understanding more about it, or other related topics, please join the 
suby-muse mailing list. It's a reasonably low traffic list, so no worries of 
being bombarded with emails.

  http://lists.berlios.de/mailman/listinfo/suby-muse

Currently, the discussion has led us into considerations of Multiple 
Inheritence. It is interesting to note that Ruby is actually but a hair's 
breath from being a type of MI language.

One last note: class A < A can be useful in and of itself for similar reasons. 
If for instance, one wished to redefine a class as an elaboration on the 
current class, as opposed to altering the class directly aliasing numerous 
methods.

-- 
T.