give thisw ruby program in golang: `class flattenarray; def self.flatten(ar); [] if ar.nil?; ar.flatten.compact; end; end` in go

main.go
package main

import (
	"fmt"
)

func flatten(ar []interface{}) []interface{} {
	if ar == nil {
		return []interface{}{}
	}

	var result []interface{}
	for _, elem := range ar {
		switch elem := elem.(type) {
		case []interface{}:
			result = append(result, flatten(elem)...)
		case nil:
			// Ignore nil values
		default:
			result = append(result, elem)
		}
	}

	return result
}

func main() {
	ar := []interface{}{[]interface{}{1, 2, []interface{}{3}}, 4, []interface{}{5, nil}, nil}
	fmt.Println(flatten(ar)) // Output: [1 2 3 4 5]
}
538 chars
31 lines