protected function executeStatic(string $class) : string
    {
        list($class, $method) = explode('::', $class);
        if (!class_exists($class)) {
            throw new \RuntimeException('could not find class: ' . $class);
        }
        if (!method_exists($class, $method)) {
            throw new \RuntimeException('could not find method in class: ' . $method);
        }
        ob_start();
        $class::$method();
        return (string)ob_get_clean();
    }