     else
       @_ended = true
       @_end callback
+  end: @::free

    @_indexOfKeys = -2
    @_ended = true

  endSync: ->
    if @_indexOfKeys?
      return @_endKeys()
    else if @_endSync

      return @_endSync()
    else
      throw new NotImplementedError()
  endSync: @::freeSync

  nextKeys: (callback) ->
    @_nexting = true
