From: "David A. Black" <dblack@...>
Date: 2007-10-07T21:39:24+09:00
Subject: Re: Is using attr_accessor for class variables possible?

Hi --

On Sun, 7 Oct 2007, Gabriel Dragffy wrote:

> I know that attr_accessor works for accessing instance variables, but it 
> doesn't seem to work for class ones. What is the best way to set/retrieve the 
> value of a class variable?

@@var = 1
@@var

:-)

If you want to wrap them in methods:

   class C
     def C.var
       @@var
     end

     def C.var=(x)
       @@var = x
     end
   end

In Rails, there's a thing called "cattr" that does this automatically:

   class C
     cattr_acccessor :var
   end

It's a little misleading, though. The term "attribute" (or attr)
refers to an attribute or property of an object. Class variables are
very promiscuous: they're shared among many objects (a class, its
descendants, all instances of all of those classes), so a class
variable is not really the right choice for an "attribute", and "attr"
is not the best name for wrappers around class variables.

If you want to represent state per class, the best way is to give your
class an instance variable or accessor:

   class C
     class << self    # C's singleton class
       attr_accessor :var
     end
   end


David

-- 
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