func Reverse(s []int) {
    s = append(s, 999)
    for i, j := 0, len(s)-1; i < j; i++ {
        j = len(s) - (i + 1)
        s[i], s[j] = s[j], s[i]
    }
}

func main() {
    s := []int{1, 2, 3}
    Reverse(s)
    fmt.Println(s) // [1 2 3]

    var a []int
    for i := 1; i <= 3; i++ {
        a = append(a, i)
    }
    Reverse(a)
    fmt.Println(a) // [999 3 2]
}

func Reverse(s []int) {
    s = append(s, 999)
    for i, j := 0, len(s)-1; i < j; i++ {
        j = len(s) - (i + 1)
        s[i], s[j] = s[j], s[i]
    }
    fmt.Printf("[in function] s:%p, first element:%p, len:%d, cap:%d\n",&s,s,len(s),cap(s))
}

func main() {
    s := []int{1, 2, 3}
    fmt.Printf("[main] s:%p, first element:%p, len:%d, cap:%d\n",&s,s,len(s),cap(s))
    Reverse(s)
    fmt.Println(s) // [1 2 3]

    var a []int
    for i := 1; i <= 3; i++ {
        a = append(a, i)
    }
    fmt.Printf("[main] a:%p, first element:%p, len:%d, cap:%d\n",&a,a,len(a),cap(a))
    Reverse(a)
    fmt.Println(a) // [999 3 2]
}

➜  [/Users/rootliu/go/src/6.824/demo] git:(master) ✗ go run demo.go
[main] s:0xc00000a060, first element:0xc000018160, len:3, cap:3
[in function] s:0xc00000a0a0, first element:0xc00001a0f0, len:4, cap:6
[1 2 3]
[main] a:0xc00000a100, first element:0xc0000181a0, len:3, cap:4
[in function] s:0xc00000a140, first element:0xc0000181a0, len:4, cap:4
[999 3 2]