Question

So I am trying out mixins and some metaprogramming in ruby and can’t get this to work for me. I want it to print “Baboon”

 module A

  def self.included(base)
      base.extend ClassMethods
  end

  module ClassMethods
    def install_A
        include InstanceMethods
    end
  end

  module InstanceMethods
      class B
         def testB
           #What goes here???
           A.monkey
         end
      end

      attr_accessor :monkey

      def initialize()
         @monkey = "baboon"
      end

      def test
          b = B.new
          puts b.testB
      end
  end
end

class Chimp
  include A
  install_A
end

c = Chimp.new
c.test

Answer 1

B is its own self-contained class. It is not associated or connected with any of the other classes or modules except to say that an instance of class B happens to be created inside of InstanceMethods::test. Declaring class B inside of the definition for module InstanceMethods limits the scope of B such that it’s not visible outside of InstanceMethods, but it doesn’t connect B and InstanceMethods in any way.

What you need is to make the module’s variable visible inside B. You can implement an initialize method for B that takes a parameter, and InstanceMethods::test can use b = B.new(@monkey) to pass the value to B (make sure B::initialize stores the value as an instance variable).