*/ final class Queue implements QueueInterface { /** * @var list */ private array $queue = []; /** * Adds a node to the queue. * * @param T $node */ public function enqueue(mixed $node): void { $this->queue[] = $node; } /** * Retrieves, but does not remove, the node at the head of this queue, * or returns null if this queue is empty. * * @return null|T */ public function peek(): mixed { return $this->queue[0] ?? null; } /** * Retrieves and removes the node at the head of this queue, * or returns null if this queue is empty. * * @return null|T */ public function pull(): mixed { return array_shift($this->queue); } /** * Dequeues a node from the queue. * * @throws Exception\UnderflowException If the queue is empty. * * @return T */ public function dequeue(): mixed { if ([] === $this->queue) { throw new Exception\UnderflowException('Cannot dequeue a node from an empty queue.'); } /** @var T */ return array_shift($this->queue); } /** * Count the nodes in the queue. * * @return int<0, max> */ public function count(): int { return count($this->queue); } }