Ilya Basov

package main

import "fmt"

func main() {

    a := []string{"Ivan", "Oleg", "Dennis"}

    fmt.Println(join(",", a...))
}

func join(sep string, l ...string) (res string) {

    for i, x := range l {

        res = res + x

        if i < len(l)-1 {
            res = res + sep
        }
    }

    return
}