From: Jeffrey Moss <jeff@...>
Date: 2005-07-12T06:04:37+09:00
Subject: class_attr_accessor

I was playing around with class variables and class instance variables 
because I wanted to implement a certain functionality, while not really 
understanding the coexistence of the two, I found the reason the two exist 
is quite clear, the class instance variables facilitate "subclass slots" (as 
I know them from other languages) while the @@ syntax facilitates "class 
slots"

I did a google search for "class_attr_accessor" and found that a number of 
people have implemented this functionality in their own code.  I suggest it 
be officially added to the ruby distribution.

Here is an example:

class Module
  private
  def class_attr_accessor(*attrs)
    attrs.each {|attr|
      module_eval(<<-EOS)
        class << self
          def #{attr}; @#{attr}; end
          def #{attr}=(v); @#{attr} = v; end
        end
      EOS
    }
  end
end

I really don't think a new notation, similar to @@, is necessary, I think 
calling obj.class.accessor_name is very nice. In fact having both a 
subclass_attr_accessor and a class_attr_accessor wouldn't hurt either. In 
that case, class_attr_accessor would just be a way to make @@vars public.

-Jeff Moss