From: Yukihiro Matsumoto <matz@...>
Date: 2005-07-07T02:19:43+09:00
Subject: Re: Inheriting Array and slice() behaviour

Hi,

In message "Re: Inheriting Array and slice() behaviour"
    on Wed, 6 Jul 2005 18:17:21 +0900, Sylvain Joyeux <sylvain.joyeux@polytechnique.org> writes:

|I have a class inheriting Array, and I expected slice() and [] 
|to return Array objects.

Why?  I'd expect them to return instances of the class of the
receiver, as Daniel does in [ruby-talk:147323], since they are ripped
part of the receiver.

|Moreover, since my Expression class has instance variables, the instance 
|produced by slice() does not have it anymore (which is bad)

I agree that is bad.  It might be possible to call initialize() at the
time of sub-array allocation, at the cost of performance.  Besides
that, we have to make consensus for how initialize() will be called
for those sub-array.

Anyway, I'd suggest you not to subclass basic classes, unless you are
sure what you're doing.  I don't think Expressions by no means have
is-a relationship to Arrays.  Inheritance is not a panacea.

							matz.