迭代时我在切片中覆盖的值更改

Question

I've got a []int that I range over. I get that when I iterate I have a key/value. I want to also access the slice which I'm iterating over. I don't understand why the slice changes however.

func main() {
var rows []string
rows = append(rows, "1  2   3", "4  5   6")
for _, row := range rows {
    row := formatRow(row)
    fmt.Println("sent row: ", row) // <------ THIS RETURNS [1,2,3]
    for i, _ := range row {
        fmt.Println("sent row: ", row) // <------ THIS RETURNS [1,3,3]
        _ = getShortRow(row, i)
    }
}
}

func getShortRow(row []int, i int) []int {
    if i == 0 {
        row := append(row[1:])
        return row
}
endPosition := i + 1
if endPosition == len(row) {
    row := append(row[:i])
    return row
}

st := append(row[:i])
end := append(row[i+1:])
row = append(st, end...)
return row
}

func formatRow(row string) []int {
    row = strings.Replace(row, "    ", ",", -1)
    if row[len(row)-1:] == "," {
        row = row[:len(row)-1]
    }
    nValues := strings.Count(row, ",") + 1
    var s []int
    // convert []string to []int
    for index := 0; index < nValues; index++ {
        var value int
        if index == nValues-1 {
            value, _ = strconv.Atoi(row)
        } else {
            commaPosition := strings.Index(row, ",")
            value, _ = strconv.Atoi(row[:commaPosition])
            row = row[commaPosition+1:]
        }
        s = append(s, value)
    }
    return s
}

I can't figure out why the slice value is [1,2,3] then [1,2,3] then [1,3,3]. It seems like it should never change.

Answer 1

Slices are reference-like types. When you pass it to some function and change contents of it there, it would change the original slice too.

I suggest you to read this and this to fully understand slices.

Your x := append(slice) won't create a new slice. Assuming you have a variable slice with type []int you could copy it with:

x := append(make([]int, 0), slice...)

or without creating an empty slice

x := append([]int(nil), slice...)

or to be more explicit

x := make([]int, len(slice))
copy(x, slice)