From: "David A. Black" <dblack@...>
Date: 2009-07-04T21:56:01+09:00
Subject: Re: How to remove/delete/destroy class variable in Ruby 1.9?

Hi --

On Sat, 4 Jul 2009, Robert Klemme wrote:

> On 04.07.2009 14:06, David A. Black wrote:
>> On Sat, 4 Jul 2009, dzw! wrote:
>> 
>>> Ok, code below shows better what I am talking about, I understand that
>>> @@var is acting like global variable.
>>> But how to get rid of it when is not needed anymore?
>
>> You're trying to maintain and alter state on a per-class basis, which
>> really means on a per-object (class object) basis. Class variables are
>> not suited to that purpose; they are, as you say, really sort of
>> vertical globals.
>> 
>> (In fact, I've always thought that $$var would be a better designation
>> for class variables than @@var, because @@var makes it look like class
>> variables have some kind of affinity with instance variables, which
>> they definitely don't.)
>
> The only commonality I can think of off the top of my head is the fact that 
> you can use them from within instances much the same way as instance 
> variables.

But you're always within an instance of something. You can access
global variables there too :-)

This is also why I don't like the "cattr_*" idiom (cattr_reader and so
on), or at least its naming. "Attribute" suggests an attribute of a
particular object. Class variables don't represent per-object state,
so they're not suited to "attribute" implementation.

>> Anyway -- I don't know of any way to undefine a class variable. I'd
>> recommend using instance variables if you need per-class state.
>
> My 0.02 EUR: the best way to get rid of class variables is to not use them in 
> the first place. :-)

I agree.


David

-- 
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