PHP arrayFlatten

class MaisraHelper
{

    /**
     * Convert a multi-dimensional array into a single-dimensional array.
     * @param $arr
     * @param $out
     * @return array
     */
    static public function arrayFlatten($arr, $out = array())
    {
        foreach ($arr as $item) {
            if (is_array($item)) {
                $out = array_merge($out, self::arrayFlatten($item));
            } else {
                $out[] = $item;
            }
        }
        return $out;
    }


}