$flatMap */ public function __construct( private readonly int $bufferSize, private readonly int $concurrency, private readonly bool $ordered, private readonly \Closure $flatMap ) { } public function __invoke(ConcurrentIterator $source): ConcurrentIterator { if ($this->concurrency === 1) { $stop = self::getStopMarker(); return new ConcurrentIterableIterator((function () use ($source, $stop): iterable { foreach ($source as $position => $value) { $iterable = ($this->flatMap)($value, $position); foreach ($iterable as $item) { if ($item === $stop) { return; } yield $item; } } })(), $this->bufferSize); } return new ConcurrentFlatMapIterator( $source, $this->bufferSize, $this->concurrency, $this->ordered, $this->flatMap, ); } }