protected static function getImplementations() {
        if (is_null(self::$implementations)) {
            self::$implementations = array(
                new FuncProxy(),
                new DataAccessControl()
            );
            
            /*
            $taoExt = \common_ext_ExtensionsManager::singleton()->getExtensionById('tao');
            self::$implementations = array();
            foreach ($taoExt->getConfig('accessControl') as $acClass) {
                if (class_exists($acClass) && in_array('oat\tao\model\accessControl\AccessControl', class_implements($acClass))) {
                    self::$implementations[] = new $acClass();
                } else {
                    throw new \common_exception_Error('Unsupported class '.$acClass);
                }
            }
            */
        }
        return self::$implementations;
    }