If you’ve adopted structured concurrency in your applications since it landed in Swift 5.5, you may have found that the ArgumentParser module does not yet work with an async main function out-of-the-box.

If you’ve used structured concurrency in Swift enough, you may have noticed that the rethrows keyword doesn’t always “work” with async/await, at least according to our intuitions about when try should and shouldn’t be required.

This article documents several techniques I have found effective at improving the run time performance of Swift applications without resorting to “writing C in .swift files”. (That is, without resorting to C-like idioms and design patterns.) It also highlights a few pitfalls that often afflict Swift programmers trying to optimize Swift code.