This week I’m at the inaugural Swift Rockies conference in Calgary and it’s been great so far. At Matt Massicotte’s lab yesterday there was a whole lot of discussion about Swift concurrency which was enlightening and fun (seriously).

Those discussions made me realize that I should share a trick that I haven’t seen mentioned anywhere yet.

Recently while migrating to Swift 6, I came across some code that was seemingly never gonna compile, no matter how many non-isolated unsafe declarations I plastered around. It’s a class called AsyncFuture that, shockingly, bridges Combine futures to async/await. So it’s not entirely unexpected that there are a lot of concurrency issues since Combine is notorious here.

My solution to this was to create a new target in that SPM package containing only AsyncFuture, and setting it to language mode 5 with a comment stating that it’ll stay there until it goes away and we migrate code off of it. Swift still supports language mode 4 so it doesn’t seem like Swift 5 will go away anytime soon at all, and this let me migrate the main target in this package to Swift 6.

Anyway, that’s it and I hope you might find it helpful. It’s a simple manoeuvre and targets are cheap in SPM, so I recommend sending any code to Swift 5 prison if it has no business playing in the Swift 6 world. Life sentence.