Sorry if I come across as the devil's advocate on this one - I think there should be another voice stating that objc use can slow a program.
Compared to C or C++, Objective C is a poor choice for performance critical code. Within performance critical zones, I will only use objc objects for very high level objects, and even then, rarely. I do use objc objects for things such as user interfaces. I've done a few ports, even for standard application level programs (omitting graphics), the difference is typically several times faster. I've made libraries which use C and C++ objects/interfaces, objc programs which are modified to use these libraries are noticeably faster. If a program needs to be fast, objc cannot compete with C or C++ objects (unless the programmer has missed important concepts of oo design or for some other unusual reason).
In short, I typically saw changes of 5 - 8 times the speed when converting class families/libraries to C++ for standard application code. That is just a change of the class' language - no complex optimizations there (other than what GCC includes), most programs can be optimized well beyond that point. I don't use objc objects for performance critical code - and, yes, I have spent much time with performance tools on this and other areas. The explanations for these differences obviously extend beyond 'how fast can a nop objc method be sent 1000 times in a row'? -- I don't need to convince anybody to use one approach over the other (it sounds like everybody is already convinced, anyhow!), I just thought I'd state that there significant gains can be made by simply avoiding objc objects in performance critical code (which back up both sides of the argument). I don't actually have hours to explain why this is so -- It shouldn't require an optimization expert to conclude (or reason) why the difference is so large. Besides, if your program needs that kind of speed, the best thing you can do is figure out why the difference exists. Other bonuses typically include significantly smaller executables and fewer exported symbols.
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