Bad API example: FileManager’s url(for:in:appropriateFor:create:)

I find FileManager‘s url(for:in:appropriateFor:create:) to be very unintuitive. It seems to have multiple, largely-orthogonal functions. It can provide paths to common folders (albeit badly). It can create temporary folders. It can locate volume-specific bins (Trash folders). It is an example of bad API design. Specifically, regarding cohesion: the principle that an API should have one… Read more

Creating files safely in Mac apps

Creating a file is a pretty basic and conceptually simple task, that many applications do (whether they realise it or not – library code often does this too, at least for temporary files such as caches or for communicating between programs). So you’d think it’d be trivial to do correctly. Alas, it is not. ☝️… Read more

Downcasting in a for loop

I sometimes forget that this is possible (and even more often exactly what the damn syntax is – kudos to vacawama in today’s case of this for reminding me with their StackOverflow answer). There are numerous other ways to write the above, but I think it is the most elegant. Inferior Alternatives More indentation, and… Read more


Explanatory diagram of frame pointers, showing a link from the x86-64 register %rbp to the start of the current frame, which holds the prior value of %rbp that points to the top of the previous frame, and so on.

This is an elaboration of a post I made in a Swift Forums thread, SE-0419: Swift Backtracing API. The question was raised whether an official Swift backtracer should try to support code that doesn’t use frame pointers. Which immediately raised the question – in my mind – of if anyone is still using the “optimisation”… Read more

NSImage is dangerous

Screenshot of an excerpt from Xcode's debug console showing the output of AddressSanitizer, having detected data race involving NSImage.

NSImage is formally documented as largely not thread-safe: The following classes and functions are generally not thread-safe. In most cases, you can use these classes from any thread as long as you use them from only one thread at a time. Check the class documentation for additional details. Apple’s Threading Programming Guide > Appendix A:… Read more

Reminder: macOS system frameworks binaries are hidden (since Big Sur)

Every now and again I’ll go to do something really innocuous with an Apple framework, like disassemble it in Hopper or check the link headers. And every. single. time. I forget that Apple did some really weird shit in Big Sur, and removed the binaries. $ ls -lh /System/Library/Frameworks/AppKit.framework/Versions/Current/AppKit ls: /System/Library/Frameworks/AppKit.framework/Versions/Current/AppKit: No such file or… Read more

SwiftUI main thread hang detector

Illustration of the MacOS Spinning Pinwheel of Death cursor

This is just a little snippet that is quite useful for reporting when your GUI thread (the main thread / actor) hangs for a significant amount of time. There are numerous heavier-weight tools for analysing this sort of thing, but I’ve found that this simple monitor does what I need most of the time. You… Read more