/**
  * Singleton.
  *
  * @since 1.0
  * @deprecated since 1.0
  *
  * @return ParamDefinitionFactory
  */
 public static function singleton()
 {
     static $instance = false;
     if ($instance === false) {
         $instance = new self();
         $instance->registerGlobals();
     }
     return $instance;
 }