From: Gennady <gfb@...>
Date: 2004-04-10T05:44:54+09:00
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.
> 
> [rolo] There are 2 things here. one Thing object and other t1 object.
> @cache is a variable that belongs to Thing or t1?

Thing is an instance of Class.
t1 is an instance of Thing.
@cash belongs to Thing and is not visible to t1 (on a side none, @@cash 
would be visible to all instances of Thing, to t1 in particular).

Gennady.

> 
> rolo
> 
> 
> 
>