How do I reverse a slice in go?

Question

How do I reverse an arbitrary slice ([]interface{}) in Go? I'd rather not have to write Less and Swap to use sort.Reverse. Is there a simple, builtin way to do this?

Answer 1

Use slices.Reverse in Go 1.21 or later:

slices.Reverse(s)

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Answers for Go version 1.20 and earlier:

The standard library does not have a built-in function for reversing a slice. Use a for loop to reverse a slice:

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

Use type parameters to write a generic reverse function in Go 1.18 or later:

func reverse[S ~[]E, E any](s S)  {
    for i, j := 0, len(s)-1; i < j; i, j = i+1, j-1 {
        s[i], s[j] = s[j], s[i]
    }
}

Use reflect.Swapper to write a function that works with arbitrary slice types in Go version 1.8 or later:

func reverse(s interface{}) {
    n := reflect.ValueOf(s).Len()
    swap := reflect.Swapper(s)
    for i, j := 0, n-1; i < j; i, j = i+1, j-1 {
        swap(i, j)
    }
}

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The functions in this answer reverse the slice inplace. If you do not want to modify the original slice, copy the slice before reversing the slice.