In an earlier post, I wrote about different ways that you can bridge your existing asynchronous code over to Swift’s new Concurrency system that leverages async / await. The mechanisms shown there work great for code where your code produces a single result that can be modeled as a single value. Since writing this post we've gained AsyncStream.makeStream which makes stream creation a lot smoother. Learn more in this post. However in some cases this isn’t possible because your existing code will provide multiple values over time. This is the case for things like download progress, the user’s current location,...

Sometimes in SwiftUI apps I’ll find that I have a model with an optional value that I’d like to pass to a view that requires a non optional value. This is especially the case when you’re using Core Data in your SwiftUI apps and use auto-generated models. Consider the following example: class SearchService: ObservableObject { @Published var results: [SearchResult] = [] @Published var query: String? } Let me start by acknowledging that yes, this object can be written with a query: String = "" instead of an optional String?. Unfortunately, we don’t always own or control the models and objects...

If you want to make sure that your code adopts Swift concurrency as correctly as possible in Swift 5.x, it's a good idea to enable the Strict Concurrency Checking (SWIFT_STRICT_CONCURRENCY) flag in your project. To do this, select your project's target and navigate to the Build Settings tab. Make sure you select All from the list of settings that is shown (Basic is the default) and type Strict Concurrency in the searchbar to find the Strict Concurrency Checking build setting. The screenshot below shows all the relevant parts for you to see: The default value for this setting is Minimal...

One of the goals of the Swift team with Swift’s concurrency features is to provide a model that allows developer to write safe code by default. This means that there’s a lot of time and energy invested into making sure that the Swift compiler helps developers detect, and prevent whole classes of bugs and concurrency issues altogether. One of the features that helps you prevent data races (a common concurrency issue) comes in the form of actors which I’ve written about before. While actors are great when you want to synchronize access to some mutable state, they don’t solve every...

UPDATE FOR XCODE 14.1: This issue appears to have been partially fixed in Xcode 14.1. Some occurences of the warning are fixed, others aren't. In this post I'm collecting situations me and others run into and track whether they are fixed or not. If you have another sample that you think is similar, please send a sample of your code on Twitter as a Github Gist. Dear reader, if you've found this page you're probably encountering the error from the post title. Let me start by saying this post does not offer you a quick fix. Instead, it serves to...

Swift 5.7 introduces many new features that involve generics and protocols. In this post, we're going to explore an extremely powerful new features that's called "primary associated types". By the end of this post you will know and understand what primary associated types are, and why I think they are extremely important and powerful to help you write better code. If your familiar with Swift 5.6 or earlier, you might know that protocols with associated types have always been somewhat of an interesting beast. They were hard to use sometimes, and before Swift 5.1 we would always have to resort...

Protocols are an extremely important part in the Swift language, and in recent updates we've received some new capabilities around protocol and generics that allow us to be much more intentional about how we use protocols in our code. This is done through the any and some keywords. In this post, you will learn everything you need to know about the similarities and differences between these two keywords. We'll start with an introduction of each keyword, and then you'll learn a bit more about the problems each keyword solves, and how you can decide whether you should use some or...

This post is up to date for Xcode 15 and newer. It supersedes a version of this post that you can find here On iOS 15, Apple granted developers the ability to present partially visible bottom sheets using a component called UISheetPresentationController. Originally, we had to resort to using a UIHostingController to bring this component to SwiftUI. With iOS 16, we don't have to do this anymore. You can make use of the presentationDetents view modifier to configure your sheets to be fully visible, approximately half visible, or some custom fraction of the screen's height. To do this, you can...

Working with dates isn’t easy. And showing them to your users in the correct locale hasn’t always been easy either. With iOS 15, Apple introduced a new way to convert Date objects from and to String. This new way comes in the form of the new Formatter api that replaces DateFormatter. As any seasoned iOS developer will tell you, DateFormatter objects are expensive to create, and therefor kind of tedious to manage correctly. With the new Formatter api, we no longer need to work with DateFormatter. Instead, we can ask a date to format itself based on our requirements in...

Closures are a powerful programming concept that enable many different programming patterns. However, for lots of beginning programmers, closures can be tricky to use and understand. This is especially true when closures are used in an asynchronous context. For example, when they’re used as completion handlers or if they’re passed around in an app so they can be called later. In this post, I will explain what closures are in Swift, how they work, and most importantly I will show you various examples of closures with increasing complexity. By the end of this post you will understand everything you need...