From: Pit Capitain <pit@...>
Date: 2005-07-08T06:25:39+09:00
Subject: Re: Inheriting Array and slice() behaviour

William Morgan schrieb:
> Excerpts from Ara.T.Howard's mail of  7 Jul 2005 (EDT):
> 
>>On Fri, 8 Jul 2005, William Morgan wrote:
>>
>>>My problem with Array#slice is that the objects created will never
>>>have #initialize called. Indeed, they never *can* have it called,
>>>because who knows what arguments need to be supplied.
>>
>>it's this simple:
> 
>  
> Actually, it's even simpler---the author of Expression can simply
> override #slice to do the right thing. The point is that the *author*
> must do this explicitly. If Ruby tries to do this automatically, it will
> return invalid objects.
> 
> In short, the current #slice behavior is a) wrong in non-trivial cases,
> b) magic, and c) inconsistent with #+ and other methods.

The LSP has been mentioned before in this thread. According to that 
principle, if someone creates a subclass of Array, you should be able to 
use the subclass like the original Array class. Array has a well defined 
#initialize method that can take zero arguments. So should the subclass, 
otherwise you're breaking the LSP. In other words, it's perfectly legal 
to call self.class.new in #slice. If Expression can't provide an 
#initialize method without arguments, it shouldn't be a subclass of Array.

Regards,
Pit