PHP enum

class PageSpecial {
    protected $value;
    private static $instances = array();
    protected function __construct($value) {
        $this->value = $value;
    }
    function __toString() {
        return $this->value;
    }
    static function conditions() {
        if (!isset($instances[__FUNCTION__])) {
            $instances[__FUNCTION__] = new self(__FUNCTION__);
        }
        return $instances[__FUNCTION__];
    }
    static function home() {
        if (!isset($instances[__FUNCTION__])) {
            $instances[__FUNCTION__] = new self(__FUNCTION__);
        }
        return $instances[__FUNCTION__];
    }
}