PMA\libraries\gis\GISPolygon::singleton PHP Method

    public static function singleton()
    {
        if (!isset(self::$_instance)) {
            $class = __CLASS__;
            self::$_instance = new $class();
        }
        return self::$_instance;
    }

 /**
  * Returns the singleton instance of geometric class of the given type.
  *
  * @param string $type type of the geometric object
  *
  * @return GISGeometry the singleton instance of geometric class
  *                          of the given type
  *
  * @access public
  * @static
  */
 public static function factory($type)
 {
     $type_lower = strtolower($type);
     $file = './libraries/gis/GIS' . ucfirst($type_lower) . '.php';
     if (!PMA_isValid($type_lower, PMA\libraries\Util::getGISDatatypes()) || !file_exists($file)) {
         return false;
     }
     if (include_once $file) {
         switch (strtoupper($type)) {
             case 'MULTIPOLYGON':
                 return GISMultipolygon::singleton();
             case 'POLYGON':
                 return GISPolygon::singleton();
             case 'MULTIPOINT':
                 return GISMultipoint::singleton();
             case 'POINT':
                 return GISPoint::singleton();
             case 'MULTILINESTRING':
                 return GISMultilinestring::singleton();
             case 'LINESTRING':
                 return GISLinestring::singleton();
             case 'GEOMETRYCOLLECTION':
                 return GISGeometrycollection::singleton();
             default:
                 return false;
         }
     } else {
         return false;
     }
 }