Go flatten slice implementation

flatten.go

package main

import (
	"fmt"
	"reflect"
)

// variadic argument to utilize Go slices expansion mechanism '...'
func flatten(input ...interface{}) (res []int) {
	for _, val := range input {
		v := reflect.ValueOf(val)

		switch v.Kind() {
		case reflect.Slice:
			// so elegant, even I got impressed by myself with this '...)...' and recursion
			res = append(res, flatten(v.Interface().([]interface{})...)...)
		case reflect.Int:
			res = append(res, v.Interface().(int))
		default:
			panic(fmt.Sprintf("incorrect input value: %s", v))
		}
	}

	return
}

func main() {
	var input = []interface{}{0, []interface{}{1, 2, []interface{}{3}}, 4}
	fmt.Println(input)
	var output []int = flatten(input)
	fmt.Println(output)
}