From: Robert Klemme <bob.news@...>
Date: 2005-07-07T06:35:45+09:00
Subject: Re: Inheriting Array and slice() behaviour

William Morgan <wmorgan-ruby-talk@masanjin.net> wrote:
> Excerpts from Sylvain Joyeux's mail of  6 Jul 2005 (EDT):
>>> What return type do you want? Arrays or Expressions? You can force
>>> return values back to Arrays with #to_a, or manually make
>>> Expressions with something like
>>>
>>>   y = Expression.new(x.slice(1..5).to_a)
>>
>> I find it VERY weird to build anything else than an Array here. Array
>> now nothing about Expression, so I don't see how - in general - it
>> could build a well-formed Expression object
>
> I agree with you. I think this is bad behavior.

I wouldn't be so certain of this.  It's normal for operations like #dup and 
#clone to behave that way.  Also, part of the smartness of ruby is that you 
can simply do self.class.new to get a new instance of the same class.  And 
often you need to create an instance of the same class.  That's not too 
abnormal.

IMHO if there is a problem then with proper initialization of the new 
instance.  OTOH, inheriting classes like Array is seldom really good.  There 
are too many methods that return plain arrays and you end up with Arrays 
anyway.  Delegation, ad hoc modification or extension with a Module is often 
better.

Kind regards

    robert