Data Structure for Subscribers

[linanqiu]

Now that the homework's due, I can finally ask this!

Addy Osmani used an array to store subscribers. This makes adding fast, but removing them a rather tedious process. He makes that better using the topic to further segment the subscribers.

I was wondering if there's a way to hash subscribers such that we store them in something like a dictionary with the key being the function, the value being a count of the number of such subscribers. Say function f has x subscribers, then whenever it gets hit, it will emit x times. Removal will simply decrement x until 0, upon which f is removed.

Is that possible? Or as a more general question, is it possible to index by functions?