Drupal 8: Redirect with a warning message

redirect_with_warning.includes.php

<?php

use Symfony\Component\HttpFoundation\RedirectResponse;

/**
 * Redirects with warning message
 *
 * When you need to redirect user upon a page load in procedural code.
 * Otherwise, use the Controller response or ...
 * ... $form_state->setRedirect('routing_machine_name'); return;
 * 
 * @param string $url
 * @param string $message
 */
function _redirect_with_warning($url, $message = NULL) {
	$response = new RedirectResponse($url, 302);
	$response->send();
	if ($message) {
		\Drupal::messenger()->addWarning($message);
	}
	exit;
}