Dir實(shí)際上是string

type Dir string

http.Dir("/public")可以認(rèn)為是類型轉(zhuǎn)換，不是函數(shù)

因?yàn)镈ir實(shí)現(xiàn)了Open接口,http.Dir("/public")將/public字符串轉(zhuǎn)換為了Dir.

// A Dir implements FileSystem using the native file system restricted to a
// specific directory tree.
//
// While the FileSystem.Open method takes '/'-separated paths, a Dir's string
// value is a filename on the native file system, not a URL, so it is separated
// by filepath.Separator, which isn't necessarily '/'.
//
// Note that Dir will allow access to files and directories starting with a
// period, which could expose sensitive directories like a .git directory or
// sensitive files like .htpasswd. To exclude files with a leading period,
// remove the files/directories from the server or create a custom FileSystem
// implementation.
//
// An empty Dir is treated as ".".
type Dir string

func (d Dir) Open(name string) (File, error) {
    ....
}

// A FileSystem implements access to a collection of named files.
// The elements in a file path are separated by slash ('/', U+002F)
// characters, regardless of host operating system convention.
type FileSystem interface {
    Open(name string) (File, error)
}

這樣看應(yīng)該比較清楚吧

http.Dir("/public")是利用本地tmp目錄實(shí)現(xiàn)一個(gè)文件系統(tǒng)；
http.FileServer(http.Dir("/public"))返回一個(gè)Handler，其用來處理訪問本地"/tmp"文件夾的HTTP請求；