concord.rb

class Concord1 < Module
  def initialize
    define_a
  end

  def define_a
    puts self
    define_method :a do | |
      puts "a"
    end
  end
end

class C1
  mod = Concord1.new
  puts mod.instance_methods.include? :a
  include mod
end

C1.new.a =>?

class Concord2 < Module
  def a
    puts "a"
  end
end

class C2
  mod = Concord2.new
  puts mod.instance_methods.include? :a
  include mod
end

C2.new.a => ?

class Concord3 < Module
  define_method :a do | |
    puts "a"
  end
end

class C3
  include Concord3.new
end

C3.new.a => ?