Of course, if you're not in void context and actually intent on returning the resulting list from processing a 10,000,000 key hash, you'll have to be able to fit that in memory anyway.
Not necessarily always the case, though. The callback routine might never return anything -- except one time when it returns one thing. A jillion-key hash in, a one-element list out.
Just like map.
You can't have your cake and eat it - you can't be using an iterator when you're concerned about memory usage.
That is patently false. In fact, the built-in hash iterator (each
) is all about efficiency -- in both space and time.
There is no reason why iterators can't be efficient.