Negative Slice Index

Why This Happens

Unlike Python, Go does not interpret negative indices as counting from the end of the slice. A negative index is always out of bounds and causes a runtime panic. Use len(s)-1 to get the last element.

The Problem

func main() {
    s := []int{1, 2, 3}
    fmt.Println(s[-1]) // runtime error: index out of range
}

The Fix

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

Step-by-Step Fix

1. 1

   Identify the negative index

   Find the line using a negative index to access a slice or array.

2. 2

   Replace with len-based access

   Use len(s)-1 for the last element, len(s)-2 for the second to last, and so on.

3. 3

   Add bounds checking

   Check that len(s) > 0 before accessing with len(s)-1 to avoid panics on empty slices.