From: "Arno J." <jub@...>
Date: 2007-08-17T18:42:22+09:00
Subject: Re: Does singleton variables have any meaning ?

unknown wrote:

> self is #<Class:A> (the singleton class of A), so @singleton_variable
> belongs to #<Class:A>.  It has no connection to A.

Ok, that's what I guessed

> #<Class:A> is the singleton class (sometimes called the "metaclass")
> of A. It's a separate object; it has its own instance variables, and
> doesn't share them with A.
> 
> As for the terminology; here:
> @var is an instance variable, and self is a class. So we can call it
> an instance variable or a class instance variable. I don't think it's
> a good idea to introduce yet another term (singleton variable) for it;
> it just gets too confusing.

I'm sorry but I still don't get it (maybe I'm a little bit nit_picking 
also)

class A
  @first_instance_var # self = A

  def meth
    @second_instance_var # self = #<A:0x2ebd140>
  end

  class << self
    @thir_instance_var # self = #<Class:A>
  end

end


All three variables are instance variables (just because of the @, as 
far as I know).
BUT, for what I've read on the web / in books
first_... would be called a "class instance variable"
second_... would be called an "instance variable"
third_... would not be called (I never met any), or would be called a 
"class instance variable" according to you, although self is not a class 
but a singleton class.

I agree that since a singleton class is some sort of class, it can be 
called a "class instance variable". But my question are "how do I access 
it ?" and "Is it any usefull" (I understand why first and second can be 
used, but not third).

> You could get indirect access to it if the object that owns it creates
> wrapper methods for it. But if you put @my_variable where your "This"
> comment is, it will be a completely different @my_variable.

I don't want to put @my_variable here, I want to use the wrapper method 
you're talking about, but I don't know how to build it :)

> David

Thank you for your time

Arno
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