NullCancellation.php

<?php

declare (strict_types=1);
namespace OpenTelemetry\SDK\Common\Future;

use Closure;
final class NullCancellation implements CancellationInterface {
    public function subscribe(Closure $callback) : string {
        return self::class;
    }
    public function unsubscribe(string $id) : void {
        // no-op
    }

}