module A
  def doit
    puts 'A doit'
  end
end
 
module B
  def doit
    puts 'B doit'
  end
end
 
module C
  def self.included(base)
    base.prepend(InstanceMethods)
  end
 
  module InstanceMethods
    def doit
      puts 'C doit'
    end
  end
end
 
module D
  def self.included(base)
    base.class_eval do
      def doit
        puts 'D doit'
      end
    end
  end
end
 
class Foo
  include A
end
 
f = Foo.new
puts Foo.ancestors.inspect
f.doit
 
puts '---- B ----'
 
# Not working
A.include(B)
puts A.ancestors.inspect
puts Foo.ancestors.inspect
f.doit
 
puts '---- C ----'
 
# Not working
A.include(C)
puts A.ancestors.inspect
puts Foo.ancestors.inspect
f.doit
 
puts '---- D ----'
 
# Working
A.include(D)
puts A.ancestors.inspect
puts Foo.ancestors.inspect
f.doit

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