design patterns in ruby

composition_and_delegation.rb

# inherite way: 
# - engine details are probably exposed to the Car
# - hard for engine-less vehicle's adaption
class Vehicle
  def start_engine
  end
  
  def stop_engine
  end
end

class Car < Vehicle
  def sunday_drive
    start_engine
    stop_engine
  end
end

# compose way
# - prevent engine-related details exposed to Vehicle
#   the only way a car can do to its engine is by working through the public interface
# - open up the possibility of other kinds of engines. (engine inheritance)
class Engine
  def start
  end
  
  def stop
  end
end

class Car
  def initialize
    @engine = Engine.new
  end
  
  def start_engine
    @engine.start
  end
  
  def stop_engine
    @engine.stop
  end
  
  def sunday_drive
    start_engine
    stop_engine
  end
end