From: dblack@...
Date: 2002-12-06T23:19:25+09:00
Subject: Re: Class-instance variables access

Hi --

On Fri, 6 Dec 2002, Ludo wrote:

> a class variable is unique for a class object
> a instance variable is unique for an instance of a class
>
> class A
>   @@uniq_for_class ## all instance see one variable
>   @one_per_instance ## each instance hold one variable
> end

Not quite.  In your example, @one_per_instance is not visible to
instances of class A.  It's an instance variable *of* class A.

  irb(main):001:0> class A
  irb(main):002:1> @var = "hello"
  irb(main):003:1> end
  "hello"
  irb(main):004:0> A.instance_variables
  ["@var"]
  irb(main):005:0> A.new.instance_variables
  []

You could make @var visible, through an accessor, but by default it's
visible only to the object whose instance variable it is -- namely,
the object A (which is a Class object).

(See also Guy D.'s further explication.)


David

-- 
David Alan Black
home: dblack@candle.superlink.net
work: blackdav@shu.edu
Web:  http://pirate.shu.edu/~blackdav