Mapping integers to booleans in Objective-C

Question

In Objective-C I need to associate a mutable collection integers (monotonic, non-contiguous, could get fairly large) to boolean values. The obvious way is just to have an NSDictionary w/ NSNumbers as keys and values.

Is there a better way that doesn't involve so much object creation? I'm really not trying to pre-optimize so much as learn if there are techniques I'm not familiar with.

This data is private to a particular class implementation, so integrating with the rest of the Cocoa APIs isn't a requirement.

Answer 1

Assuming you're happy with your integers being pointer-sized, you can use NSMapTable (also comes with a C API) or CFDictionary (which is toll-free bridged to NSDictionary).

Or, of course, you could use a (non-CF/Cocoa) C or C++ data structure, but it wouldn't integrate with Cocoa quite as cleanly.

Answer 2

The general case of mapping one scalar to another isn't something Cocoa handles that well, because it's focused on objects and scalars need to be wrapped before it has anything to offer. But in the case of booleans, there are only two possible mapped states, so that opens up a pretty handy way of doing it: NSIndexSet. Presence in the set = boolean state.