RouteSubscriberBase.php

<?php

namespace Drupal\Core\Routing;

use Symfony\Component\EventDispatcher\EventSubscriberInterface;
use Symfony\Component\Routing\RouteCollection;

/**
 * Provides a base implementation for RouteSubscriber.
 */
abstract class RouteSubscriberBase implements EventSubscriberInterface {
    
    /**
     * Alters existing routes for a specific collection.
     *
     * @param \Symfony\Component\Routing\RouteCollection $collection
     *   The route collection for adding routes.
     */
    protected abstract function alterRoutes(RouteCollection $collection);
    
    /**
     * {@inheritdoc}
     */
    public static function getSubscribedEvents() : array {
        $events[RoutingEvents::ALTER] = 'onAlterRoutes';
        return $events;
    }
    
    /**
     * Delegates the route altering to self::alterRoutes().
     *
     * @param \Drupal\Core\Routing\RouteBuildEvent $event
     *   The route build event.
     */
    public function onAlterRoutes(RouteBuildEvent $event) {
        $collection = $event->getRouteCollection();
        $this->alterRoutes($collection);
    }

}