From: "David A. Black" <dblack@...>
Date: 2004-04-10T04:13:03+09:00
Subject: Re: Cache of objects

Hi --

On Sat, 10 Apr 2004, rolo wrote:

> -----Original Message-----
> From: Joel VanderWerf [mailto:vjoel@PATH.Berkeley.EDU]
> Sent: Friday, April 09, 2004 11:58 PM
> To: ruby-talk ML
> Subject: Re: Cache of objects
> 
> 
> rolo wrote:
> > class Thing
> >    @cache = {}
> >    def self.instance(name)
> >      @cache[name] ||= new(name)
> >    end
> >    def initialize(name)
> >      @name = name
> >    end
> > end
> > 
> > t1 = Thing.instance "t"
> > t2 = Thing.instance "t"
> > 
> > p t1.id
> > p t2.id
> > 
> > 
> > [rolo] mysterious. it works! but since cache is an instance level variable how is it shared amongst all the class instances?
> 
> @cache is an instance variable of the class Object called Thing. It's 
> just a regular instance variable, but it happens to be stored in a class 
> object instead of in instances of the class. Instances of Thing can't 
> access it directly.
> 
> [rolo] should it not be @@cache ?

No, that's a class variable, which is different from an instance
variable of a Class object.  In spite of the shared use of '@',
they're separate and different things.


David

-- 
David A. Black
dblack@wobblini.net