NSNumber vs Int

Question

If integers cannot be written to a dictionary and then to a .plist, but NSNumbers can is it better to use NSNumbers throughout the app, rather than needing to convert every-time saving or loading a dictionary from a .plist?

Answer 1

As a generalization: Just stick with POD types until you need to use an object based representation, such as NSNumber. The performance is much better with the PODs, but you'll need NSNumber in some cases.

In some cases, it may make sense to use NSNumber instead -- this is typically when you reuse a NSNumber often -- this is to avoid making a ton of duplicate NSNumbers. Such occurrences are practical only rarely beyond serialization and generic objc interfaces (bindings, transformers, dictionaries).

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Update/Details: The ObjC runtime will in some cases, on some architectures, and on some OS versions substitute a tagged pointer representing NSNumbers of specific type and domain. Although the internal representation has changed since originally written a few years back, here is a good introduction to the subject: http://objectivistc.tumblr.com/post/7872364181/tagged-pointers-and-fast-pathed-cfnumber-integers-in. Where this can be used, it saves you from slow operations like allocations, locking, and ref count ops. Nevertheless, tagged pointers are incapable of representing every number and it introduces overhead, so you should still favor basic builtins over NSNumber as a default. Tagged pointers are a great optimization where applicable, but are far from competing with the builtins when you just need a number.