go type string的用法

package main

import "fmt"

type DD string

const (
   C DD = "dd"
   D DD = "cc"
)

func (DD) JoinString() DD  {
   return C + D
}

func main() {
   C.JoinString()
   D.JoinString()
   var c DD
   c.JoinString()
   
   var m = make(map[DD]interface{})
   m[C] = `netstat -r`
   m[D] = `ifconfig`

   if t, ok := m[C]; !ok {
      panic(t)

   } else {
      fmt.Println(t)
   }

}