GO os.File 的疑问

go 标准库中的 os.File 内部实现如下：

type File struct {
	*file // os specific
}

type file struct {
	pfd         poll.FD
	name        string
	dirinfo     *dirInfo // nil unless directory being read
	nonblock    bool     // whether we set nonblocking mode
	stdoutOrErr bool     // whether this is stdout or stderr
	appendMode  bool     // whether file is opened for appending
}

我的疑问是，为什么不直接用下面的方式

type File struct {
	pfd         poll.FD
	name        string
	dirinfo     *dirInfo // nil unless directory being read
	nonblock    bool     // whether we set nonblocking mode
	stdoutOrErr bool     // whether this is stdout or stderr
	appendMode  bool     // whether file is opened for appending
}