Класс фильтрации (готовый ООП)

class Filter {
    /**
     * @param $string
     * @return mixed
     */
    function clearFullSpecialChars ($string) {
        $string = filter_var($string, FILTER_SANITIZE_FULL_SPECIAL_CHARS);
        return $string;
    }

    /**
     * @param $string
     * @return string
     */
    function output ($string) {
        $string = $this->clearFullSpecialChars($string);
        $string = nl2br($string);
        return $string;
    }

    /**
     * @param $string
     * @return mixed
     */
    function clearString ($string) {
        $string = filter_var($string, FILTER_SANITIZE_STRING);
        return $string;
    }

    /**
     * @param $string
     * @return int
     */
    function clearInt ($string) {
        $string = filter_var($string, FILTER_SANITIZE_NUMBER_INT);
        $string = intval(abs($string));
        return $string;
    }
}