public function has_any(array $keys) {
        $maxtime = 0;
        if ($this->ttl != 0) {
            $maxtime = cache::now() - $this->ttl;
        }

        foreach ($keys as $key) {
            if (isset($this->store[$key]) && ($this->ttl == 0 || $this->store[$key][1] >= $maxtime)) {
                return true;
            }
        }
        return false;
    }