From: Luke Kanies <luke@...>
Date: 2005-07-12T09:53:44+09:00
Subject: Re: class_attr_accessor

On Tue, 12 Jul 2005, Jeffrey Moss wrote:

> The @@class_var syntax is unique in that you can assign a value to a class
> and it is propogated down.

Yep, I know, and I almost never use this type of variable.

> With class instance vars, class << self; attr_accessor :class_var; end
> this will only give you a "slot", you still have to populate the slot with
> something.  So for a subclass to inherit values, it would need to have
> something populating the subclasses values each time the class is inherited
> presumably in the "inherited" method or manually as in Ara's "init" method.
> The same goes for an instance attribute, it needs to be initialized in the
> initialize method, presumably, you can't assign defaults with the
> attr_accessor method.

Yeah, I know how the variable type behaves; as I said, I'm using tons of
them.

In my case, I've got classes set up that are perfectly functional with
only class instance variables defined, but they can define extra methods
if they want.  For instance:

    # an abstract base class
    class Base
        def self.dostuff
            unless defined? @data
                raise "Data must be defined
            end
            ... do stuff ...
        end
    end

    class Sub < Base
        @data = %w{this is data}
    end

    class OtherSub < Base
        @data = %w{this is more data}
    end

I use this basic construct over and over, but I'm using it almost to
death in my current project which is right about 10k lines now.

-- 
One of the Ten Commandments for Technicians
        (7) Work thou not on energized equipment, for if thou dost, thy
            fellow workers will surely buy beers for thy widow and
            console her in other ways.
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Luke Kanies | http://reductivelabs.com | http://config.sage.org