private function compute(string $expression): int
    {
        // catch anything which could be a security issue
        if (0 !== preg_match("/[^\d.+*%^|&~<>\/()-]/", $this->expression)) {
            throw new \InvalidArgumentException('Wrong value in error types config value:' . $this->expression);
        }

        return 0 + (int)eval('return ' . $expression . ';');
    }