mixin_polymorphism.rb

module DefaultAutomobileProperties
  def engine_type
    :gasoline
  end
  
  def front_wheel_drive
    true
  end
  
  def passengers
    2
  end
  
  def removable_top
    false
  end
end

class Truck
  include DefaultAutomobileProperties
  def engine_type
    :diesel
  end
end

class Wrangler
  include DefaultAutomobileProperties
  def front_wheel_drive
    false
  end
  def removable_top
    true
  end
end

truck = Truck.new
wrangler = Wrangler.new

truck.engine_type          # => :diesel
truck.front_wheel_drive    # => true
truck.passengers           # => 2
truck.removable_top        # => false
wrangler.engine_type       # => :gasoline
wrangler.front_wheel_drive # => false
wrangler.passengers        # => 2
wrangler.removable_top     # => true

polymorphism.rb

class Automobile

  def engine_type
    :gasoline
  end

  def front_wheel_drive
    true
  end

  def passengers
    2
  end

  def removable_top
    false
  end
end

class Truck < Automobile
  def engine_type
    :diesel
  end
end

class Wrangler < Automobile
  def front_wheel_drive
    false
  end
  def removable_top
    true
  end
end

truck = Truck.new
wrangler = Wrangler.new

truck.engine_type          # => :diesel
truck.front_wheel_drive    # => true
truck.passengers           # => 2
truck.removable_top        # => false
wrangler.engine_type       # => :gasoline
wrangler.front_wheel_drive # => false
wrangler.passengers        # => 2
wrangler.removable_top     # => true