iphone/objective-c: using singleton class as a container for globals

Question

So I'm finding that I'm using a singleton User class to access global variables throughout an iphone app. In some cases I use the instance in almost all the methods within a class. So in the first few lines of each method I have statement such as:

User *user = [User sharedManager];

This is obviously not a very DRY implementation. My question is: instead of repeating this statement in all the methods I need to access User can't I just instantiate this once, say in the initializer, and then set a property equal to this pointer such as:

-(id)init {
.....
self.sharedUser = [User sharedManager];
....
}

and then reference this property in each method instead of instantiating the singleton?

Answer 1

sure, you can do this. There might be (small) issues with code readability, but there's nothing wrong with this.

Answer 2

Why not just introduce a global that points to your singleton instead. Whilst its "less pure", you are trading off end-user performance. self.sharedUser.sharedValue will have exactly the same run-time cost as [[User sharedManager] sharedValue]

Dot notation for properties is about the stupidest thing that was ever added to Objective-C - it confuses the crap out of people who think its someway more efficient.

Now, if you meant self->sharedUser->sharedValue then you would be avoiding the property-method lookup and using two pointer-deferences instead - thats going to be about as fast as having globalUser->sharedValue, but has the added overhead of needing a new pointer in every instance of every class that wants to access the globals.