mixed $cancellable:
public function enqueue($cancellable) : void { if (!\is_object($cancellable) || !\method_exists($cancellable, 'then') || !\method_exists($cancellable, 'cancel')) { return; } $length = \array_push($this->queue, $cancellable); if ($this->started && 1 === $length) { $this->drain(); } }