code: func Uuid() string {
  	b := make([]byte, 16)
  	_, _ = io.ReadFull(rand.Reader, b)
  	b[6] = (b[6] & 0x0F) | 0x40
  	b[8] = (b[8] &^ 0x40) | 0x80
  	return fmt.Sprintf("%x-%x-%x-%x-%x", b[:4], b[4:6], b[6:8], b[8:10], b[10:])
  }
docs: /*
  	Uuid returns a type 4 UUID.
  */