emberjs mistery setter

gistfile1.coffee

App.TimeInputComponent = Ember.Component.extend(
  MAX_TIME: 99 * 60 + 59

  didInsertElement: () ->
    if @get('value')
      @set('inputValue', @formatValue(@get('value')))

  classNames: ['time-input-component']
  classNameBindings: ['focused:focused']

  digits: []

  keyUp: (e) ->
    code = e.which
    char = String.fromCharCode(code)
    return unless 48 <= code <= 57 or code == 8 or code == 9

    digits = @get('digits')
    if code == 8
      digits.shift()
    else if char.match(/[0-9]/)
      digits.pop() if digits.length >= 4
      digits.unshift(char)
    # Need this to sync the values of the array in the component's this[META_KEY].values
    @set('digits.0', digits[0])
    @set('digits.1', digits[1])
    @set('digits.2', digits[2])
    @set('digits.3', digits[3])
    
    
    
##
#  digits has it's own digits[META_KEY].values that are set initially on object creation.
#
#  withouth the 4 set() calls, digits[META_KEY].values don't change,
#  so doing a get('digits.3') in the template to show it will return `undefined`
#
#  -- what's the answer to a better implementation of this?