Class error with foreach?

If I define a class thus:

class item {
    // some variables go here

    public function add() {
         // some code goes here
         return $result;
    }
}

$things = new item;
foreach($things as $thing) {
    $retval = $thing->add();
}

I find that the IDE doesn't seem to see add as a method of the item class but reports it as unkown.

Am I doing this wrong or is it a bug in PHPStorm?