Devise\Support\Sortable\Sort::get_random_string PHP Method

    protected function get_random_string($length, $valid_chars = 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ')
    {
        $string = "";
        $num_valid_chars = strlen($valid_chars);
        for ($i = 0; $i < $length; $i++) {
            $random_pick = mt_rand(1, $num_valid_chars);
            $random_char = $valid_chars[$random_pick - 1];
            $string .= $random_char;
        }
        return $string;
    }