golang 生成伪随机数

func GenerateUnique() string {
    var r = []rune("abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMnopQRSTUVWXYZ0")
    uniq := make([]rune,20)
    for i := range uniq {
        rand.Seed(time.Now().UTC().UnixNano() + int64(i<<20))
        uniq[i] = r[rand.Intn(len(r))]
    }
    return string(uniq)
}