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Extending Specific Objects with Modules (written by Phil Tomson)
CodeExpectedActual
class Person
  attr_reader :name, :age, :occupation
  def initialize(name, age, occupation)
    @name, @age, @occupation = name, age, occupation
  end    
  def mild_mannered?
    true
  end
end
jimmy = Person.new('Jimmy Olsen', 21, 'cub reporter')
clark = Person.new('Clark Kent', 35, 'reporter')
jimmy.mild_mannered?
 true true 
clark.mild_mannered?
 true true 
module SuperPowers
  def fly
    'Flying!'
  end
  def leap(what)    
    "Leaping #{what} in a single bound!"
  end
  def mild_mannered?
    false
  end
  def superhero_name
    'Superman'
  end
end
clark.extend(SuperPowers)
clark.superhero_name
 "Superman" "Superman" 
clark.fly
 "Flying!" "Flying!" 
clark.mild_mannered?
 false false 
jimmy.mild_mannered?
 true true 
class Person  
  extend SuperPowers
end
#which is equivalent to:
Person.extend(SuperPowers)
Person.superhero_name
 "Superman" "Superman" 
Person.fly
 "Flying!" "Flying!"