What phpdoc syntax do I use for Iterators in phpstorm?

Given the following iterator:

class foo implements Iterator
{
     /**
      * @return bool
      */
     public function current()
     {
     }
}

I then create an instance:

$x = new bla;

foreach($x as $y)
{
     echo $y;
}

phpstorm is unable to tell me that $y is a boolean.

I actually need to do this with objects instead of booleans, but I suppose the phpdoc construct would be the same.

Anyone any idea how to tell phpstorm what an iterator holds in it's array, without doing so at each location it's used?