MainActor by Default code example
Asked on 2025-08-01
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To see a code example of using MainActor by default, you can refer to the session titled "Embracing Swift concurrency" from WWDC 2025. In this session, they discuss how protecting code with the main actor by default is driven by a build setting, which is enabled by default for new app projects created with Xcode 26. They provide an example of adding a method to an image model to fetch and display an image from a URL, which runs on the main thread in one piece. You can find this discussion starting at the Embracing Swift concurrency (04:31) mark.
Embracing Swift concurrency
Join us to learn the core Swift concurrency concepts. Concurrency helps you improve app responsiveness and performance, and Swift is designed to make asynchronous and concurrent code easier to write correctly. We’ll cover the steps you need to take an app through from single-threaded to concurrent. We’ll also help you determine how and when to make the best use of Swift concurrency features – whether it’s making your code more asynchronous, moving it to the background, or sharing data across concurrent tasks.
Code-along: Elevate an app with Swift concurrency
Learn how to optimize your app’s user experience with Swift concurrency as we update an existing sample app. We’ll start with a main-actor app, then gradually introduce asynchronous code as we need to. We’ll use tasks to optimize code running on the main actor, and discover how to parallelize code by offloading work to the background. We’ll explore what data-race safety provides, and work through interpreting and fixing data-race safety errors. Finally, we’ll show how you can make the most out of structured concurrency in the context of an app.
What’s new in Swift
Join us for an update on Swift. We’ll talk about workflow improvements that make you more productive, and new and modernized library APIs for fundamental programming tasks. We’ll show examples of Swift adoption throughout more layers of the software stack. Finally, we’ll explore new language features for both improving approachability of concurrency, and achieving peak performance when you need it.