Why does ARC retain method arguments?

Question

When compiling with ARC, method arguments often appear to be retained at the beginning of the method and released at the end. This retain/release pair seems superfluous, and

Answer 1

Even the answer of soul is correct, it is a bit deeper than it should be:

It is retained, because the passed reference is assigned to a strong variable, the parameter variable. This and only this is the reason for the retain/release pair. (Set the parameter var to __weak and what happens?)

One could optimize it away? It would be like optimizing every retain/release pairs on local variables away, because parameters are local variables. This can be done, if the compiler understands the hole code inside the method including all messages sent and functions calls. This can be applied that rarely that clang even does not try to do it. (Imagine that the arg points to a person (only) belonging to a group and the group is dealloc'd: the person would be dealloc'd, too.)

And yes, not to retain args in MRC was a kind of dangerous, but typically developers know their code that good, that they optimized the retain/release away without thinking about it.