From: Devin Mullins <twifkak@...>
Date: 2005-07-08T22:17:06+09:00
Subject: Re: Inheriting Array and slice() behaviour

Pit Capitain wrote:

> See http://en.wikipedia.org/wiki/Liskov_substitution_principle for a 
> short definition. According to this principle, the subclass doesn't 
> have to have exactly the same initialize as the parent class, but it 
> has to support at least the same interface.

Wrong. The LSP says that /objects/ of a subtype have to support the same 
interface. That is, it specifically ignores the constructor. That's how 
Java gets away with not inheriting the constructor.

Of course, Ruby *does* inherit the constructor, so you can just tell 
people that want to derive from Array not to define initialize, or to do 
it in a way that doesn't suck, as you mentioned in the rest of your email.

In that case, I suggest what I suggested previous:

>Array has a "copy constructor" (Array.new can take another Array), so you could call klass.new(theNewSubArray) unless klass == Array, instead of just massaging it into a klass...
>
But in truth, I agree most with William Morgan:

>In short, the current #slice behavior is a) wrong in non-trivial cases,
>b) magic, and c) inconsistent with #+ and other methods.
>
Devin
Sorry to shout "Wrong," like that. It's just I get so few opportunities 
to be absolutely confident in my answer. :)