Kraken\Event\EventEmitterInterface::once PHP Метод

    public function once($event, callable $listener);

 /**
  * @see EventEmitterInterface::once
  */
 public function once($event, callable $listener)
 {
     $handler = $this->emitter->once($event, $listener);
     return new EventListener($this, $handler->getEvent(), $handler->getHandler(), $handler->getListener());
 }