Go slice flatten

package main

import (
	"errors"
	"fmt"
)

func main() {
	fmt.Println(`[1,2,3] -> [1,2,3]`)
	input := []interface{}{1, 2, 3}
	result, err := Flatten(input)
	fmt.Println(result, err)

	fmt.Println(`[1,2,[3],4] -> [1,2,3,4]`)
	input = []interface{}{1, 2, []int{3}, 4}
	result, err = Flatten(input)
	fmt.Println(result, err)

	fmt.Println(`[[1,2,[3]],4] -> [1,2,3,4]`)
	input = []interface{}{[]interface{}{1, 2, []int{3}}, 4}
	result, err = Flatten(input)
	fmt.Println(result, err)

	fmt.Println(`[[1,2,[3]],[[1,2,3],4]] -> [1,2,3,1,2,3,4]`)
	input = []interface{}{1, 2, []int{3}, []interface{}{[]int{1, 2, 3}, 4}}
	result, err = Flatten(input)
	fmt.Println(result, err)
}

// Flatten flattens an array of arbitrarily nested arrays of integers into a flat array of integers. e.g. [[1,2,[3]],4] -> [1,2,3,4].
func Flatten(input interface{}) (result []int, err error) {
	result = []int{}

	// check by input type
	switch t := input.(type) {

	// if int array, append
	case []int:
		result = append(result, t...)
		return

	// if int, append
	case int:
		result = append(result, t)
		return

	// if []interface{}, do Flatten recursively
	case []interface{}:
		for _, i := range t {
			_result, _err := Flatten(i)
			if _err != nil {
				err = _err
				return
			}

			result = append(result, _result...)
		}

	// else throw error since type is not supported
	default:
		err = errors.New("wrong array type")
	}

	return
}