Question

I’m writing an objective-C game and I’m at the stage where i should start optimising some of my code in the game loops.
I have an extensive amount of class compare methods used,

if ([obj isMemberOfClass:[SomeClass class]])

etc.
I heard this sort of checking is quite expensive, because I choose only to have 1 array populated with multiple classes, I need some sort of class check.
I was thinking perhaps that adding a property to NSObject subclassing NSObject to contain a string property, that during initialisation i would make equal to the class name of that particular subclass. Then simply doing a

if ([obj.klass isEqualTo:@”SomeClass”])

Would this be beneficial?
I’m trying to keep as much dynamic coding out of the game loops as possible.

Thanks!

Answer 1

Short answer: no. String comparison is prohibitively more expensive compared to other methods of comparing (or: classifying, categorizing) objects.

Long answer: don’t optimize what you haven’t analyzed, measured and compared. What you really want to do before you start optimizing is to get a clear picture of how your app behaves and what its performance bottlenecks are. The change you’re attempting is unlikely to lead to any noticeable change in performance, so I suggest to first find the real bottlenecks.

In this particular case, sending isEqual to an NSString is 4 times slower than isMemberOfClass if the test fails. And such conditional tests fail most of the time, which is why you should ignore the results of the test succeeding.

The successful string comparison is fast because it’s a simple pointer comparison, if two strings are equal it is likely that they point to the same memory address. If they’re not equal, then each character in the string will be compared for equality, probably by using the hash method.

Here are the results of the Object Comparison tests that I added to my performance test project. You can use that project to make further tests.