Fooling around with Ruby includes and extends in classes and modules

classes.rb

#!/usr/bin/ruby

HashA = {a: 1, b: 2}
HashB = {b: 3, c: 4}
HashC = {c: 5, d: 6}

module Modules
  module ModuleA
    def self.included base
      base.class_eval do
        extend ClassMethods
      end
      base.class.class_eval do
        attr_accessor :foo_hash
      end
    end

    def new_instance_method
      true
    end

    def foo_hash
      self.class.foo_hash
    end

    module ClassMethods
      def new_class_method
        true
      end

      def set_hash hash
        self.foo_hash = hash
      end
    end
  end
end

module Classes
  class ClassA
    include Modules::ModuleA
    set_hash HashA
  end

  class ClassB < ClassA
    set_hash HashB
  end

  class ClassB::ClassC
  end
end

instance_a = Classes::ClassA.new
instance_b = Classes::ClassB.new
instance_c = Classes::ClassB::ClassC.new
instance_d = Class.new Classes::ClassB

puts "instance_b.class:", instance_b.class
puts "instance_d.class:", instance_d.class
puts "instance_a.foo_hash:", instance_a.foo_hash
puts "instance_b.foo_hash:", instance_b.foo_hash

instance_e = Classes::ClassB.dup.new
puts "instance_e.class (before const_set):", instance_e.class
Classes::const_set 'ClassF', instance_e.class
Classes::ClassF.set_hash HashC
instance_f = Classes::ClassF.new

puts "instance_e.class (after const_set):", instance_e.class
puts "instance_f.class:", instance_e.class
puts "instance_b.foo_hash (after ClassB.dup):", instance_b.foo_hash
puts "instance_f.foo_hash:", instance_f.foo_hash

puts "Classes::ClassB.respond_to?(:new_class_method) == true",
  Classes::ClassB.respond_to?(:new_class_method) == true
puts "Classes::ClassB.respond_to?(:new_instance_method) == false",
  Classes::ClassB.respond_to?(:new_instance_method) == false
puts "instance_b.respond_to?(:new_class_method) == false",
  instance_b.respond_to?(:new_class_method) == false
puts "instance_b.respond_to?(:new_instance_method) == true",
  instance_b.respond_to?(:new_instance_method) == true
puts "instance_d.respond_to?(:new_class_method) == false",
  instance_d.respond_to?(:new_class_method) == false
puts "instance_d.respond_to?(:new_instance_method) == true",
  instance_d.respond_to?(:new_instance_method) == true
puts "instance_e.respond_to?(:new_class_method) == false",
  instance_e.respond_to?(:new_class_method) == false
puts "instance_e.respond_to?(:new_instance_method) == true",
  instance_e.respond_to?(:new_instance_method) == true
puts "instance_f.respond_to?(:new_class_method) == false",
  instance_f.respond_to?(:new_class_method) == false
puts "instance_f.respond_to?(:new_instance_method) == true",
  instance_f.respond_to?(:new_instance_method) == true