define_method on modules

non-working.rb

#!/usr/bin/ruby1.8

class Main
        module Extra
                def self.define_fancy_method(method_name)
                        define_method(method_name) do |arg|
                                return [arg, arg].join(self.separator)
                        end
                end
        end

        module M1
                extend Extra

                Extra.define_fancy_method :foo
        end

        module M2
                extend Extra

                Extra.define_fancy_method :faa
        end

        include M1
        include M2

        attr_accessor :separator
end

x = Main.new
x.separator = ','
puts x.foo('a') # => 'a,a'
puts x.faa('b') # => 'b,b'

working.rb

#!/usr/bin/ruby1.8

class Main
        module M1
                def self.define_fancy_method(method_name)
                        define_method(method_name) do |arg|
                                return [arg, arg].join(self.separator)
                        end
                end

                define_fancy_method :foo
        end

        module M2
                # copy and pasted from M1
                def self.define_fancy_method(method_name)
                        define_method(method_name) do |arg|
                                return [arg, arg].join(self.separator)
                        end
                end

                define_fancy_method :faa
        end

        include M1
        include M2

        attr_accessor :separator
end

x = Main.new
x.separator = ','
puts x.foo('a') # => 'a,a'
puts x.faa('b') # => 'b,b'