I fixed a rather nasty bug today in AspectObjectiveC. One particular unit test would crash with EXC_BAD_ACCESS every time. After learning far more about registers and ABIs than I ever wanted to know (thanks, Greg Parker), it dawned on me that performSelector: was corrupting memory. It was particularly hard to track down because the crash would happen a couple of lines after the call to performSelector:, when the corrupted memory was actually accessed.

I've never had a problem with performSelector: before, but this time I was using it a little differently. The return value of the selector was an NSRect.

Now for the gory explanation.