golang 中 path 包的 Dir 和 Join

package main

import (
    "fmt"
    "path"
)

func main() {
    fmt.Println(" :", path.Dir(""))
    fmt.Println(". :", path.Dir("."))
    fmt.Println("a :", path.Dir("a"))
    fmt.Println("/ :", path.Dir("/"))
    fmt.Println("/a :", path.Dir("/a"))
    fmt.Println("/a/b/ :", path.Dir("/a/b/"))
    fmt.Println("/a/b :", path.Dir("/a/b"))
    fmt.Println("a/b :", path.Dir("a/b"))
    fmt.Println("a/b/ :", path.Dir("a/b/"))
    fmt.Println("/// :", path.Dir("///"))
    fmt.Println("///a :", path.Dir("///a"))
}
————————————————
 : .
. : .
a : . 
/ : /
/a : /
/a/b/ : /a/b
/a/b : /a
a/b : a
a/b/ : a/b
/// : /
///a : /

package main

import (
    "fmt"
    "path"
)

func main(){
    fmt.Println(", :", path.Join("", ""))
    fmt.Println("/, :", path.Join("/", ""))
    fmt.Println(", / :", path.Join("", "/"))
    fmt.Println("/, / :", path.Join("/", "/"))
    fmt.Println("/a, :", path.Join("/a", ""))
    fmt.Println(", /a :", path.Join("", "/a"))
    fmt.Println("/a, / :", path.Join("/a", "/"))
    fmt.Println("/, /a :", path.Join("/", "/a"))
    fmt.Println("a, b :", path.Join("a", "b"))
    fmt.Println("/a, /b :", path.Join("/a", "/b"))
    fmt.Println(", // :", path.Join("", "//"))
    fmt.Println("//,  :", path.Join("//", ""))
    fmt.Println(", /a :", path.Join("", "/a"))
    fmt.Println("/a, :", path.Join("/a", ""))
    fmt.Println("/a, /b :", path.Join("/a", "/b"))
    fmt.Println("a, /b :", path.Join("a", "/b"))
    fmt.Println("/a, /b :", path.Join("/a", "/b"))
}
————————————————
, : 
/, : /
, / : /
/, / : /
/a, : /a
, /a : /a
/a, / : /a
/, /a : /a
a, b : a/b
/a, /b : /a/b
, // : /
//,  : /
, /a : /a
/a, : /a
/a, /b : /a/b
a, /b : a/b
/a, /b : /a/b