.coffee

prop = (obj, props) ->
  for prop, getset of props
    if getset.get
      obj.__defineGetter__ prop, -> getset.get.apply obj, arguments
    if getset.set
      obj.__defineSetter__ prop, -> getset.set.apply obj, arguments

class SomeCar
  constructor: ->
    _doors = 4
    _seats = 2
    _seatsTaken = 0
    prop @,
      doors:
        get: -> _doors
      seats:
        get: -> _seats
      seatsTaken:
        get: -> _seatsTaken
        set: (val) ->
          throw new Error "There are not enough seats" if val > _seats
          _seatsTaken = val



car = new SomeCar()
car.seatsTaken = 2 # success
car.seatsTaken = 4 # error