From: Gary Wright <gwtmp01@...>
Date: 2009-03-03T07:05:01+09:00
Subject: Re: Delegating class methods


On Mar 2, 2009, at 9:24 AM, lasitha wrote:
> There is a school of thought that eigenclass [1] instance variables
> are generally preferred over  @@class_variables.  Folks coming to ruby
> from other languages often miss the distinction but you'll find many
> exposés on this [2], including in the Pickaxe.
>
> I personally like eigenclass variables - they provide all the
> capability of class variables, fit elegantly into ruby's object model
> and follow all the rules of instance variables. So i don't ever bother
> with class vars.

I don't think I've ever seen the term 'eigenclass variables' used in
this way.  Every object has instance variables.  Classes are objects
and so they have instance variables.  There is no need to talk about
eigen classes (or the more common term, singleton classes) when you
are talking about alternatives to class variables.

The main confusion with Ruby class variables comes from:
   -- Ruby class variables have syntax similar to instance variables
      but much different semantics
   -- Ruby class variables are assumed to be analogous to C++ class
      variables (or Java class variables) but that is the wrong
      analogy. Ruby instance variables of class objects is the more
      appropriate comparison.

It would be nice if there was a common term for 'instance variables
of class objects' but 'eigenclass variables' isn't it.

Gary Wright