php mysqli问题

Hey, I am having a heck of a time trying to get something to work. Hopefully someone can help me out!

So I have a mysqli class as such:

class mysqli {

    public static $mysqli2;
    public function __construct(){}

    static function con(){
        if(!self::$mysqli2){
            self::$mysqli2 = new mysqli(DB_HOST, DB_USER, DB_PASS, DB_NAME);
        }
        return self::$mysqli2;
    }
}

which I can access from another function by doing something like:

gd::con()->prepare(...)

However I am having trouble accessing this from another class which I have. How can this be done, that is, accessing this function from this mysqli class, from within another class? Thanks!

Your can't create class mysqli, because there is one standart