From: Florian Gross <flgr@...>
Date: 2005-03-31T04:54:44+09:00
Subject: Re: Defining a Class Accessor

Navindra Umanee wrote:

> Florian Gross <flgr@ccan.de> wrote:
> 
>>Do you really need to use @@variables? From my experience they tend to 
>>cause trouble.
> 
> Could you explain why they would cause trouble?

I thought the original post would answer that well enough already, but 
in my own Ruby experience I have so far being surprised when using them. 
Why should they be used when you can use far simpler constructs with 
clearer rules?

Generally they seem to be used most as a quick replacement for instance 
variables when something goes wrong without further questioning or 
actually finding the root of the problem. I've seen them used quite 
frequently in this case:

module StackMixIn
   def push(item)
     @items << item
   end

   def pop()
     @items.pop
   end

   # I'd like to initialize @items, but this will not work:
   @items = []

   # If I just replace every '@items' with '@@items' it will magically
   # work. It's an obvious fix. It must be in Ruby exactly as a fix for
   # this kind of situation.
end

(And yes, I know that they are going to be simplified in Rite, but I'm 
not sure if that is going to make them completely non-surprising to most 
people...)