func Reverse(s string) string {
  runes := []rune(s)
  for i, j := 0, len(runes)-1; i < j; i, j = i+1, j-1 {
    runes[i], runes[j] = runes[j], runes[i]
  }
  return string(runes)
}

package strings

import (
 "sync"
 "unicode/utf8"
)

const threshold = 100  // This value needs to be discussed

var runePool = sync.Pool{
 New: func() interface{} {
  return make([]rune, 0, threshold)
 },
}

// Reverse returns the inverted string of s.
// Implemented through slice inversion, directly 
// inverting bytes for small strings.
// Using rune array inversion for large strings.
func Reverse(s string) string {
 if len(s) == 0 {
  return ""
 }

 if len(s) < threshold {
  // Short string direct inversion
  bytes := []byte(s)
  for i, j := 0, len(bytes)-1; i < j; i, j = i+1, j-1 {
   bytes[i], bytes[j] = bytes[j], bytes[i]
  }
  return string(bytes)
 }

 // Inverting Long Strings with a Run Array
 runes := runePool.Get().([]rune)
 runes = runes[:0]
 runes = append(runes, []rune(s)...)
 
 for i, j := 0, len(runes)-1; i < j; i, j = i+1, j-1 {
  runes[i], runes[j] = runes[j], runes[i]
 }
 s = string(runes)
 runePool.Put(runes)
 return s
}