Objective-C: when to use function vs method

Question

I've started using Xcode's refactoring abilities (edit > refactor > extract) and noticed that Xcode offers to extract a method or a function.

I've read here and elsewhere about the differences between the two and understand that a method is connected to a class while a function is not. So I'm not looking for definitions, please.

Assuming that no arguments are involved, when is it appropriate to use one instead of the other? I understand that if something isn't really about the class then it could be a function but again, that's just about the definitions. I'm looking for good ol' use cases.

In my personal case, I'm trying to refactor some code out of the AppDelegate's applicationDidEnterBackground. As it is the only place to handle events upon entering the background, the only way to clean up the code is to extract subroutines into .. well, functions. But they'd be inside AppDelegate.m so wouldn't they be methods?

Hmmm..

Answer 1

Personally, I only use functions if, and only if, the following two requirements are met:

1. I use it so frequently within a given class, or throughout the project, that it warrants being generalized.
2. It has no side-effects or context dependancies (none of that void *context mess).

In my opinion, C-style functions should only be used as a last resort or in cases where you truly need functional behavior within this kind of an application. Event handling is both application-specific, and context sensitive, so it's best if you left that alone and focused on refactoring common patterns out.