Beginning meta-programming question

ruby-talk
1

I'm pretty new to ruby, and just playing around. I can't work out why the
following won't work, though:

   1. module TrackInheritors
   2. def self.extended(parent)
   3. class << parent
   4. puts self
   5. @@inheritors = []
   6.
   7. def self.inheritors
   8. @@inheritors
   9. end
   10.
   11. def self.inherited(child)
   12. @@inheritors << child
   13. end
   14. end
   15. end
   16. end
   17.
   18. class Parent
   19. extend TrackInheritors
   20. end
   21.
   22. class Child1 < Parent
   23. end
   24.
   25. class Child2 < Parent
   26. end
   27.
   28. puts Parent.inheritors
   29.
   30. # -:28: undefined method `inheritors' for Parent:Class
   (NoMethodError)

2

When you open the singleton class of parent, you don't need to define
the methods for "self.", just define them directly, cause you are
already on the singleton class:

module TrackInheritors
  def self.extended(parent)
    class << parent
      puts self
      @@inheritors =

      def inheritors
        @@inheritors
      end

      def inherited(child)
        @@inheritors << child
      end
    end
  end
end

class Parent
   extend TrackInheritors
end

class Child1 < Parent
end

class Child2 < Parent
end

puts Parent.inheritors

$ ruby inheritors.rb
#<Class:Parent>
Child1
Child2

I'm not really sure where were you defining those methods, in the
singleton class of the singleton class?

Jesus.

···

On Mon, Jul 26, 2010 at 6:48 AM, Andrew Wagner <wagner.andrew@gmail.com> wrote:

I'm pretty new to ruby, and just playing around. I can't work out why the
following won't work, though:

1. module TrackInheritors
2. def self.extended(parent)
3. class << parent
4. puts self
5. @@inheritors =
6.
7. def self.inheritors
8. @@inheritors
9. end
10.
11. def self.inherited(child)
12. @@inheritors << child
13. end
14. end
15. end
16. end
17.
18. class Parent
19. extend TrackInheritors
20. end
21.
22. class Child1 < Parent
23. end
24.
25. class Child2 < Parent
26. end
27.
28. puts Parent.inheritors
29.
30. # -:28: undefined method `inheritors' for Parent:Class
(NoMethodError)