public function add(HolidayData $holidayData) { $this->collection[$holidayData->getYear()][$holidayData->getMonth()][$holidayData->getDay()] = $holidayData; ksort($this->collection[$holidayData->getYear()][$holidayData->getMonth()]); ksort($this->collection[$holidayData->getYear()]); ksort($this->collection); return $this; }