When you turn on strict concurrency checking or you start using the Swift 6 language mode, there will be situations where you run into an error that looks a little bit like the following: Main actor-isolated property can not be referenced from a Sendable closure What this error tells us is that we're trying to use something that we're only supposed to use on or from the main actor inside of a closure that's supposed to run pretty much anywhere. So that could be on the main actor or it could be somewhere else. The following code is an example...

When Apple released Xcode 16 last year, they made the Swift 6 compiler available along with it. This means that we can create new projects using Swift 6 and its compile-time data race protections. However, the big question for many developers is: Is 2025 the right time to adopt Swift 6 fully, or should we stick with Swift 5 for now? In this post, I won’t give you a definitive answer. Instead, I’ll share my perspective and reasoning to help you decide whether adopting Swift 6 is right for you and your project(s). The right answer depends on loads of...

With Swift 6, we have an entirely new version of the language that has all kinds of data race protections built-in. Most of these protections were around with Swift 5 in one way or another and in Swift 6 they've refined, updated, improved, and expanded these features, making them mandatory. So in Swift 5 you could get away with certain things where in Swift 6 these are now compiler errors. Swift 6 also introduces a bunch of new features, one of these is the sending keyword. Sending closely relates to Sendable, but they are pretty different in terms of why...

Once you start migrating to the Swift 6 language mode, you'll most likely turn on strict concurrency first. Once you've done this there will be several warings and errors that you'll encounter and these errors can be confusing at times. I'll start by saying that having a solid understanding of actors, sendable, and data races is a huge advantage when you want to adopt the Swift 6 language mode. Pretty much all of the warnings you'll get in strict concurrency mode will tell you about potential issues related to running code concurrently. For an in-depth understanding of actors, sendability and...

When you create a new Swift Package in Xcode 16, the Package.swift contents will look a bit like this: // swift-tools-version: 6.0 // The swift-tools-version declares the minimum version of Swift required to build this package. import PackageDescription let package = Package( name: "AppCore", products: [ // Products define the executables and libraries a package produces, making them visible to other packages. .library( name: "AppCore", targets: ["AppCore"]), ], targets: [ // Targets are the basic building blocks of a package, defining a module or a test suite. // Targets can depend on other targets in this package and products from...

Once you start migrating to the Swift 6 language mode, you'll most likely turn on strict concurrency first. Once you've done this there will be several warings and errors that you'll encounter and these errors can be confusing at times. I'll start by saying that having a solid understanding of actors, sendable, and data races is a huge advantage when you want to adopt the Swift 6 language mode. Pretty much all of the warnings you'll get in strict concurrency mode will tell you about potential issues related to running code concurrently. For an in-depth understanding of actors, sendability and...

Once you start migrating to the Swift 6 language mode, you'll most likely turn on strict concurrency first. Once you've done this there will be several warings and errors that you'll encounter and these errors can be confusing at times. I'll start by saying that having a solid understanding of actors, sendable, and data races is a huge advantage when you want to adopt the Swift 6 language mode. Pretty much all of the warnings you'll get in strict concurrency mode will tell you about potential issues related to running code concurrently. For an in-depth understanding of actors, sendability and...

Once you start migrating to the Swift 6 language mode, you'll most likely turn on strict concurrency first. Once you've done this there will be several warings and errors that you'll encounter and these errors can be confusing at times. I'll start by saying that having a solid understanding of actors, sendable, and data races is a huge advantage when you want to adopt the Swift 6 language mode. Pretty much all of the warnings you'll get in strict concurrency mode will tell you about potential issues related to running code concurrently. For an in-depth understanding of actors, sendability and...

Once you start migrating to the Swift 6 language mode, you'll most likely turn on strict concurrency first. Once you've done this there will be several warings and errors that you'll encounter and these errors can be confusing at times. I'll start by saying that having a solid understanding of actors, sendable, and data races is a huge advantage when you want to adopt the Swift 6 language mode. Pretty much all of the warnings you'll get in strict concurrency mode will tell you about potential issues related to running code concurrently. For an in-depth understanding of actors, sendability and...

In Xcode 16, this error actually is sometimes presented as "Passing closure as a 'sending' parameter risks causing data races between code in the current task and concurrent execution of the closure". The cause is the exact same as what's covered in this post. Once you start migrating to the Swift 6 language mode, you'll most likely turn on strict concurrency first. Once you've done this there will be several warnings and errors that you'll encounter and these errors can be confusing at times. I'll start by saying that having a solid understanding of actors, sendable, and data races is...