One of the major advantages of iterators is that they can produce items one at a time, which can be very significant if the items are expensive to produce and you don't need all of them, or you don't want the upfront cost all at once. Since, as others have said, foreach generally operates on a list, it doesn't seem the most efficient approach to convert an iterator to a list. Consider for example processing the results of HTTP API calls: do you want to first do a ton of HTTP calls, store the results, and then process them, or do you want to process each result as it comes in?

Another thing to consider is that the number of items returned from an iterator may not be known - it may even be infinite!* If you, for example, tie an iterator to an array, using that array in a foreach will cause it to actually iterate over the items returned from the iterator one-by-one, but it will also call FETCHSIZE to find out how many items there are.

So my question would be: why do you want to use an iterator in a foreach instead of while?

(BTW, personally I like Iterator::Simple a little bit better than Iterator. You may also be interested in how I implemented a really simple iterator, including an overloading of the <> operator, in my Algorithm::Odometer::Gray.)

* Update: To preempt any questions about what good an infinite iterator is: they can be used in operations like islice or zip.