Join

Returns a string by concatenating all of the elements in the collection, separated by the specified separator string.

• Use reflect.ValueOf() to get the array or slice and the separator string, make() to create an appropriate string slice.
• Use a for loop with Value.Len() and Value.Index() to iterate over each element, fmt.Sprintf() to convert it to a string.
• Use strings.Join() to combine the strings using the separator provided.

import (
    "fmt"
    "reflect"
    "strings"
)

func Join(params ...interface{}) string {
    arr, sp := reflect.ValueOf(params[0]),
        reflect.ValueOf(params[1]).String()
    ars := make([]string, arr.Len())

    for i := 0; i < arr.Len(); i++ {
        ars[i] = fmt.Sprintf("%v", arr.Index(i))
    }

    return strings.Join(ars, sp)

}

Join([]int{1, 2, 3}, ".") // "1.2.3"