Example on how to create join function for int64 - originally created it here: https://play.golang.org/p/KpdkVS1B4s

int64_join.go

package main

import (
	"fmt"
	"strconv"
)

func UJoin(list []uint64, sep string) string {
	length := len(list)

	if length == 0 {
		return ""
	}

	if length == 1 {
		return strconv.FormatUint(list[0], 10)
	}

	s := ""

	for i, item := range list {
		s = s + strconv.FormatUint(item, 10)

		if i < length-1 {
			s = s + sep
		}
	}

	return s
}

func Join(list []int64, sep string) string {
	length := len(list)

	if length == 0 {
		return ""
	}

	if length == 1 {
		return strconv.FormatInt(list[0], 10)
	}

	s := ""

	for i, item := range list {
		s = s + strconv.FormatInt(item, 10)

		if i < length-1 {
			s = s + sep
		}
	}

	return s
}

func main() {
	a := []int64{1, 5, 4, 12}

	fmt.Println("Join: ", Join(a, ", "))
}