Objective-C properties - is using [self myProperty] or self.myProperty slower than myProperty?

Question

I'm using Objective-C properties to handle retaining/releasing instance variables for me. In my class, i'm doing stuff like this:

self.myProperty = somethingIWantToRetain
[self.myProperty doSomeAction]
[self.myProperty doSomethingElse]

Is using [self myProperty] / self.myProperty slower than simply using myProperty for those lines where i'm not changing the value of myProperty? Eg would the following be faster?

self.myProperty = somethingIWantToRetain
[myProperty doSomeAction]
[myProperty doSomethingElse]

Thanks

Answer 1

It's almost certainly a little bit slower, but it's unlikely to matter much.

Referring to your ivar directly (with a naked myProperty) accesses the variable directly. Referring to your property getter (with the equivalent self.myProperty or [self myProperty]) has to invoke a method, which will generally perform a retain and autorelease on your ivar.

However, method dispatch in Objective-C is very, very fast, and the retain/autorelease calls are pretty cheap as well, especially for objects that will likely not be destroyed when the autorelease pool is cleared. I would focus on readability and consistent style, and only worry about performance here when it becomes clear that you have performance bottlenecks to chase.