// {f1,f2} -> f2(f1(
func getComposeIndexFuncsLeft(funcs []string) string {
    if nil == funcs || len(funcs) == 0 {
        return ""
    }
    // reverse
    sort.Sort(sort.Reverse(sort.StringSlice(funcs))) // 有點繞
    bb := new(bytes.Buffer)
    // foreach
    for _, f := range funcs {
        bb.WriteString(f)
        bb.WriteString("(")
    }
    return bb.String()
}

// {f1,f2} -> ))
func getComposeIndexFuncsRight(funcs []string) string {
    if nil == funcs || len(funcs) == 0 {
        return ""
    }
    bb := new(bytes.Buffer)
    // foreach
    size := len(funcs)
    for i := 0; i < size; i++ {
        bb.WriteString(")")
    }
    return bb.String()
}

Reverse 逆序?qū)崿F(xiàn):

func reverse(s [] interface) [] interface {
    for i, j := 0, len(s)-1; i < j; i, j = i+1, j-1 {
        s[i], s[j] = s[j], s[i]
    }
    return s
}