How to reverse a slice in Go

Reverse a Slice in Golang
Created
Modified

Using a for Loop

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

package main

import "fmt"

func main() {

  s := []string{"b", "c", "d"}

  for i := len(s)/2 - 1; i >= 0; i-- {
    s[i], s[len(s)-1-i] = s[len(s)-1-i], s[i]
  }

  fmt.Printf("%q\n", s)
}
["d" "c" "b"]

The same thing, except with two indices:

package main

import "fmt"

func main() {

  s := []string{"b", "c", "d"}

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

  fmt.Printf("%q\n", s)
}
["d" "c" "b"]

Using reflect.Swapper Function

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

package main

import (
  "fmt"
  "reflect"
)

func main() {

  s := []string{"b", "c", "d"}

  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)
  }

  fmt.Printf("%q\n", s)
}
["d" "c" "b"]

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.

Using Type Parameters

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]
  }
}

Related Tags

#reverse# #slice#

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