From: Rick DeNatale <rick.denatale@...>
Date: 2010-05-06T22:34:00+09:00
Subject: Re: Class variable "scope"

2010/5/6 Vinícius Baggio Fuentes <vinibaggio@gmail.com>:
> Hi all,
>
> I've been writing a library for me to play with metaprogramming as an
> exercise, but then I got stuck
> on a non-metaprogramming issue:
>
> ## a.rb
> class A
>  def self.add_something(*sth)
>    @@my_things ||= []
>    @@my_things << sth
>  end
>
>  def self.my_things
>    @@my_things
>  end
> end
>
> ## b.rb
> require 'a'
>
> class B < A
>  add_something :bag, :boots
> end
> require 'a'
>
> ## c.rb
> class C < A
>  add_something :sword, :shield
> end
>
> The result, when requiring both c and b into an irb shell is, as expected:
>
> ruby-1.8.7-p249 > C.my_things
>  => [[:bag, :boots], [:sword, :shield]]
> ruby-1.8.7-p249 > B.my_things
>  => [[:bag, :boots], [:sword, :shield]]
>
> I did achieve the following:
>
> C.my_things
> [[:sword, :shield]]
> B.my_things
> [[:bag, :boots]]
>
> by moving my_things method into each child class and using the method on the
> add_something method, but there must be a better way. How one could improve
> this?

Use a class instance variable rather than a class variable.

Also I suspect you really want to get [:sword, :shield] rather than
[[:sword, :shield]]

class A
 def self.add_something(*sth)
   @my_things ||= []
   @my_things.concat sth
 end

 def self.my_things
   @my_things
 end
end


class B < A
 add_something :bag, :boots
end

class C < A
 add_something :sword, :shield
end

B.my_things # => [:bag, :boots]
C.my_things # => [:sword, :shield]

If you really want to get a array of arrays rather than a single level
array, just change the .concat back to <<


HTH
-- 
Rick DeNatale

Blog: http://talklikeaduck.denhaven2.com/
Github: http://github.com/rubyredrick
Twitter: @RickDeNatale
WWR: http://www.workingwithrails.com/person/9021-rick-denatale
LinkedIn: http://www.linkedin.com/in/rickdenatale