RejectedPromise example

    public function sendAsyncRequest(RequestInterface $request): HttplugPromise
    {
        if (!$promisePool = $this->promisePool) {
            throw new \LogicException(sprintf('You cannot use "%s()" as the "guzzlehttp/promises" package is not installed. Try running "composer require guzzlehttp/promises".', __METHOD__));
        }

        try {
            $response = $this->sendPsr7Request($request, true);
        } catch (NetworkException $e) {
            return new HttplugPromise(new RejectedPromise($e));
        }

        $waitLoop = $this->waitLoop;

        $promise = new GuzzlePromise(static function D) use ($response, $waitLoop) {
            $waitLoop->wait($response);
        }, static function D) use ($response, $promisePool) {
            $response->cancel();
            unset($promisePool[$response]);
        });