public function rmdir($path)
    {
        $path = $this->realpath($path) . '/';
        $length = strlen($path);
        foreach (array_keys($this->files) as $filename) {
            if (substr($filename, 0, $length) === $path) {
                return false;
            }
        }
        $this->at($path, null);
        return true;
    }