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Issue 42

🤔 Swift 6 compiler vs Swift 6 language mode!

I have recently learned that some of the breaking changes that will come with Swift 6 (like full data isolation and data race safety checks) will be part of the Swift 6 language mode, which will be an opt-in feature in the Swift 6 compiler.

This means that, when you update your version of Xcode or use a Swift toolchain that uses the Swift 6 compiler, unless you explicitly enable the Swift 6 language mode, your code will be compiled using the Swift 5 language mode.

I personally did not know about this difference until recently and it certainly takes some time pressure off me and it means that I will be able to rejig some priorities accordingly.

The Engineering manager of the Swift language team at Apple Holly Borla has recently been on Dave Verwer and Sven A. Schmidt’s podcast Swift Package Indexing providing a lot of context about the Swift 6 release and certainly answering a lot of questions and putting a lot of worries about Swift’s next major release at ease that I’m sure a lot of iOS developers like me had about the new language mode!

CI/CD providers latest software versions

Latest available Xcode and macOS versions on popular mobile CI/CD providers.

Xcode Cloud

15.4 (15F31d)

14.5 (23F79)


15.4 (15F31d)



15.4 (15F31d)


GitHub Actions

15.4 RC (15F31c)



15.4 (15F31d)



15.4 (15F31d)


🔍 Comparing Appcircle and Bitrise: Which DevOps Tool Builds Faster? (Sponsored)

In the fast-paced world of mobile app development, build time is a game changer. Lengthy build times disrupt workflows and slow down progress.

AppCircle has put a lot of effort into improving its build caching performance by introducing new caching implementation methods that provide a more reliable and efficient compilation environment. In this article, they compare their new implementation’s performance with Bitrise caching.

📦 Build a Swift Package with the Swift 6 language mode

On the 15th of March, the Swift language team created the release branch for Swift 6. As part of the release process and to allow users to test their apps and packages on Swift 6, they are also making snapshots from this branch regularly available for download.

As I said in this issue’s introduction, building with the Swift 6 compiler does not necessarily mean building with the Swift 6 Language Mode. Learn about installing the toolchain and enabling the language mode in this article on my blog.

🛸 Win a FREE lifetime Indie subscription to Emerge Tools

If you have been a subscriber of the newsletter for a while, you will know that I am a big fan of Emerge Tools and the amazing stuff that they ship for mobile app developers.

They have recently announced a new subscription plan for Indie developers that I will definitely be buying and, to celebrate the announcement, they are giving away 5 lifetime subscriptions to this plan for FREE! Make sure you check out their post and comment with the App Store link for your app to enter the giveaway!

🔨 Xcode 15.4 is out!

A new public stable version of Xcode is out with a lot of bug fixes and improvements from the previous version. As always, when a new release is out, I take some time to update the CI/CD service support at the top of this newsletter.

🎉 The new version is widely supported across the board already!

👀 How to monitor Xcode Build times with RocketSim

RocketSim is a must-have companion for your simulator that simplifies tasks such as comparing designs with your implementation, changing the simulator’s location, sending deep links and even creating recordings with touches & audio.

If these features weren’t convincing enough, Antoine has now added support for caching builds and monitoring your build and compilation times over time, even comparing between different Xcode versions! 💪

🐌 Why does fetching SPM packages take so long?

I thoroughly enjoyed reading this article by Ahmad Yasser on why adding a Swift Package Manager dependency is slow. It turns out that Apple does a full clone of the package’s repository instead of a shallow clone, which is a more expensive request on GitHub’s side and can result in rate limiting of requests.

To tackle this issue and make the load more bearable on clients, some companies with big repositories are applying a workaround that Ahmad Yasser goes through in this article 👏.