public function getTypes()
    {
        $handlers = &gplcart_static('price.rule.types');

        if (isset($handlers)) {
            return $handlers;
        }

        $handlers = gplcart_config_get(GC_FILE_CONFIG_PRICE_RULE_TYPE);
        $this->hook->attach('price.rule.types', $handlers, $this);
        return $handlers;
    }