How to Reverse a Slice in Go: Simple Guide and Example

To reverse a slice in Go, you swap elements from the start and end moving towards the center using a loop. Use for with two indexes, swapping slice[i] and slice[j] until they meet or cross.

Syntax

To reverse a slice in Go, use a for loop with two indexes: one starting at the beginning (i) and one at the end (j). Swap the elements at these positions and move i forward and j backward until i is no longer less than j.

go

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

Example

This example shows how to reverse a slice of integers. It prints the original slice, reverses it using the swapping method, and then prints the reversed slice.

go

package main

import "fmt"

func main() {
    nums := []int{1, 2, 3, 4, 5}
    fmt.Println("Original slice:", nums)

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

    fmt.Println("Reversed slice:", nums)
}

Output

Original slice: [1 2 3 4 5]
Reversed slice: [5 4 3 2 1]

Common Pitfalls

One common mistake is trying to reverse the slice by creating a new slice without copying elements properly, which can cause unexpected results or extra memory use. Another is forgetting to update both indexes i and j in the loop, causing an infinite loop or no reversal.

go

package main

import "fmt"

func main() {
    nums := []int{1, 2, 3, 4, 5}
    // Wrong: forgetting to update j
    for i := 0; i < len(nums)/2; i++ {
        nums[i], nums[len(nums)-1-i] = nums[len(nums)-1-i], nums[i]
    }
    fmt.Println("Reversed slice:", nums)

    // Right way:
    nums = []int{1, 2, 3, 4, 5}
    for i, j := 0, len(nums)-1; i < j; i, j = i+1, j-1 {
        nums[i], nums[j] = nums[j], nums[i]
    }
    fmt.Println("Correctly reversed slice:", nums)
}

Output

Reversed slice: [5 4 3 2 1]
Correctly reversed slice: [5 4 3 2 1]

Quick Reference

• Use two indexes: start (i) and end (j).
• Swap elements at i and j.
• Move i forward and j backward until they meet.
• Works for slices of any type.

Key Takeaways

Reverse a slice by swapping elements from start and end moving inward.

Use a for loop with two indexes to swap elements until they meet or cross.

Always update both indexes in the loop to avoid infinite loops.

This method works in-place without extra memory allocation.

You can reverse slices of any data type using this approach.