/**
  * The singleton method
  *
  * @return Cardwall_Semantic_CardFieldsFactory an instance of the factory
  */
 public static function instance()
 {
     if (!isset(self::$instance)) {
         $class_name = __CLASS__;
         self::$instance = new $class_name();
     }
     return self::$instance;
 }
 /**
  * @see TRACKER_EVENT_GET_SEMANTIC_FACTORIES
  */
 public function tracker_event_get_semantic_factories($params)
 {
     $params['factories'][] = Cardwall_Semantic_CardFieldsFactory::instance();
 }