Expanded class hierarchy of SessionHandler in Drupal 8
- class \Drupal\Core\Session\SessionHandler extends \Symfony\Component\HttpFoundation\Session\Storage\Proxy\AbstractProxy implements \Drupal\Core\Session\SessionHandlerInterface uses DependencySerializationTrait
- class \Drupal\mongodb_user\MongodbSessionHandler implements \Drupal\mongodb_user\SessionHandlerInterface