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);
  }

}