unit.coffee

class Unit

  @create: (options) ->
    # This is the object which will hold the private data.
    privData = {}

    # We create a new unit and pass it the privData object.
    unit = new Unit privData, options

    # Wrap all methods and pass privData as the first argument. This incurs
    # minimal overhead because we only have to create wrappers while the
    # actual method stays the same and can be shared between instances.
    for name, method of Unit.prototype
      unit[name] = ->
        args = Array.prototype.slice.call arguments
        args.unshift privData
        method.apply @, args

    # Return the new object.
    return unit

  # Here you can put private data into privData and nobody will have access to
  # it. Properties added to @ will be publicly readable and writeable.
  constructor: (privData, options) ->
    privData.x = options.x || 0; privData.y = options.y || 0;
    @publicData = 42

  move: (privData, x, y) ->
    privData.x += x; privData.y += y;
    console.log "Moved to #{privData.x} #{privData.y}"
    console.log @publicData


unit = Unit.create { x: 1, y: 2 }
unit.publicData = -1
unit.move -2, 7