Looking for advice on this and it's best if I present an example to explain...

I have a ShoppingCart object that holds many Items.

The item object has a flag isPerishable

When I get the object ShoppingCart I would like to know how many Item objects it holds are of type isPerishable, the only way I know how to do that it is to add a howManyIsPerishable() method to the ShoppingCart object and loop over the Items and count on the isPerishable flag.

Is there a more intelligent way of doing this?

Thanks