How to assign a value to the empty slice after the declaration

Question

I am trying to assign a value to the empty slice as follows.

func main() {
    var s []int
    fmt.Println(s, len(s), cap(s))
    s[0] = 99
}

And it throws an exception,

panic: runtime error: index out of range

Note: I know one way of doing this by initializing the value at declaration part as follows. But in the above example I am trying to assign a value after the declaration.

var s []int{99}

Is there a way to achieve this?

Answer 1

Empty slices cannot just be assigned to. Your print statement shows that the slice has length and capacity of 0. Indexing at [0] is definitely out of bounds.

You have (at least) three choices:

• Append to the slice: s = append(s, 99)
• or Initialize the slice to be non-empty: s := make([]int, 1)
• or Initialize your slice with the element you want: s := []int{99}

You can find tutorials on slices in the Go tour, or a lot more details about slice usage and internals.