Object Oriented Features

• modules define namespaces (like 'package' in Perl)

  • module StateMachine
      class State
        def initialize(name)
          @name = name
        end
        ...
      end
      RESET_STATE = State.new('reset') #module const
      def reset
        @current_state = RESET_STATE
      end
      def transition(nextState)
        ...  
      end
    end
    

• Single inheritance with mixins
  • modules are mixed in to classes to add features

    • class MyStateMachine
        include StateMachine
        def initialize
          reset
        end
      end
      

• modules and classes always open (even the built-in ones)

  • class Array #add a rotate! method to built-in Array
      def rotate!
        self.unshift( self.pop)
        return self[0]
      end
    end
    a = [1,2,3,4,5]
    a.rotate! #a -> [5,1,2,3,4]
    

• singleton methods: specializing an object

  • a = [1,2,3,4,5]
    def a.rotate!
      self.unshift( self.pop)
      return self[0]
    end
    a.rotate! #a -> [5,1,2,3,4]