Using Closures as controllers in Symfony

ControllerListener.php

<?php

namespace AppBundle\EventListener;

use Symfony\Component\HttpKernel\Event\GetResponseEvent;

class AppControllerListener
{
    public function onKernelRequest(GetResponseEvent $event)
    {
        $request = $event->getRequest();

        $route = $request->attributes->get('_route');
        $routeDefinitions = include dirname(__DIR__).'/routes.php';

        if (isset($routeDefinitions[$route])) {
            $request->attributes->set('_controller', $routeDefinitions[$route]['controller']);
        }
    }
}

routes.php

<?php

use Symfony\Component\HttpFoundation\Response;

return [
    'app_default_index' => [
        'path' => '/',
        'controller' => function () {
            return new Response('A Closure Controller');;
        },
    ],
];

routing.php

<?php

use Symfony\Component\Config\Resource\FileResource;
use Symfony\Component\Routing\RouteCollection;
use Symfony\Component\Routing\Route;

/** @var \Symfony\Component\Routing\Loader\PhpFileLoader $loader */
$path = $loader->getLocator()->locate('@AppBundle/routes.php');
$routeDefinitions = include $path;

$collection = new RouteCollection();
$collection->addResource(new FileResource($path));

foreach ($routeDefinitions as $name => $definition) {
    $collection->add($name, new Route($definition['path']));
}

return $collection;

routing_dev.yml

_closure:
    resource: "@AppBundle/Resources/config/routing.php"

services.yml

services:
    app.event_listener.controller:
        class: AppBundle\EventListener\ControllerListener
        tags:
            - { name: 'kernel.event_listener', event: 'kernel.request', method: 'onKernelRequest', priority: 31 }

Or an other solution would be to use RouteCollectionBuilder to load the routes like it's done in the MicroKernel.