Kraken\Event\BaseEventEmitterTrait::once PHP Method

    public function once($event, callable $listener)
    {
        if (!isset($this->eventListeners[$event])) {
            $this->eventPointers[$event] = 0;
            $this->eventListeners[$event] = [];
        }
        $pointer =& $this->eventPointers[$event];
        $eventListener = new EventListener($this, $event, $listener, $this->attachOnceListener($pointer, $event, $listener));
        $this->eventListeners[$event][$pointer++] = $eventListener;
        return $eventListener;
    }