Sibling rivalry and class variables

On Mon, Aug 12, 2002 at 02:05:45AM +0900, Kent Dahl wrote:
> Because class variables are some kind of wierd black magic. Once a class
> variable comes into existance, it is available to all instances of the
> class and subclasses. I.e. it is available downwards in the inheritance
> hierarchy.
> 
> When you don't make the @@data variable until the subclass, it does not
> propagate back up to the superclass. Beware, this path may lead to
> madness:

So I see...

--- begin classvar.rb ---
class Parent
    @@name = "I'm the parent."
    def initialize
        puts @@name
    end
end

class Son < Parent
    @@name = "I'm the son."
end

class Daughter < Parent
    @@name = "I'm the daughter."
end

Son.new      # => I'm the daughter.
Daughter.new # => I'm the daughter.
--- end ---

This behavior is downright counterintuitive to me. The class
"Daughter" has managed to affect the behavior of the class "Son", but
"Daughter" is not an ancestor of "Son".

What would you guys suggest I do if I want a variable set in the
parent that the child may or may not override? So far, I've had to
resort to using instance variables instead, like this:

class Parent
    def initialize
        @name = "I'm the parent."
    end
end

class Son
    def initialize
        super
        @name = "I'm the son."
    end
end

class Daughter
    def initialize
        super
        @name = "I'm the daughter."
    end
end

This doesn't seem to be the right way to do things though, since with
the way I'm using @name, it's a variable whose value will be the same
across all instances of the same class.

Thoughts?