When you start learning about actors in Swift, you’ll find that explanations will always contain something along the lines of “Actors protect shared mutable state by making sure the actor only does one thing at a time”. As a single sentence summary of actors, this is great but it misses an important nuance. While it’s true that actors do only one thing at a time, they don’t always execute function calls atomically. In this post, we’ll explore the following: Exploring what actor reentrancy is Understanding why async functions in actors can be problematic Generally speaking, you’ll use actors for objects...

On of app development’s largest downsides (in my opinion) is that it’s frustratingly hard for developers to quickly iterate on an app’s core features due to the App Review process which can take anywhere between a few hours to a few days. As a result of this process, developers either need to ship their apps with A/B testing built in if they want to test multiple variations of a feature, they can iterate more slowly or they can opt to build a so-called backend-driven UI. A backend-driven UI is a user interface that’s drawn by fetching information about the UI...

It’s common for developers to leverage protocols as a means to model and abstract dependencies. Usually this works perfectly well and there’s really no reason to try and pretend that there’s any issue with this approach that warrants an immediate switch to something else. However, protocols are not the only way that we can model dependencies. Often, you’ll have a protocol that holds a handful of methods and properties that dependents might need to access. Sometimes, your protocol is injected into multiple dependents and they don’t all need access to all properties that you’ve added to your protocol. Also, when...

A while ago I’ve published a post that explains how you can use AsyncStream to build your own asynchronous sequences in Swift Concurrency. Since writing that post, a new approach to creating AsyncStream objects has been introduced to allow for more convenience stream building. In this post, I’ll expand on what we’ve already covered in the previous post so that we don’t have to go over everything from scratch. By the end of this post you will understand the new and more convenient makeStream method that was added to AsyncStream. You’ll learn how and when it makes sense to build...

When you work with CI, you’ll know how frustrating it can be when a CI server has versions of Xcode or other tools installed than the tools that you’re using. Especially major Xcode releases can be problematic. If your CI doesn’t have the same new versions available while your project uses recently released features which will lead your builds to fail. An obvious example of this would be when you start using features that are exclusive to the latest iOS version. If Xcode doesn’t know about these features then your project won’t build. An out of date CI can cause...

The long awaited iOS 17.4 and iPadOS 17.4 have just been released which means that we could slowly but surely start seeing alternative app stores to appear if you’re an EU iOS user. Alongside the 17.4 releases Apple has made Xcode 15.3 and Swift 5.10 available. There’s not a huge number of proposals included in Swift 5.10 but that doesn’t make this release less significant. With Swift 5.10, Apple has managed to close some large gaps that existed in Swift Concurrency’s data safety features. In short, this means that the compiler will be able to catch more possible thread safety...

When you’re decoding JSON, you’ll run into situations where you’ll have to decode dates every once in a while. Most commonly you’ll probably be dealing with dates that conform to the ISO-8601 standard but there’s also a good chance that you’ll have to deal with different date formats. In this post, we’ll take a look at how you can leverage some of Swift’s built-in date formats for en- and decoding data as well as providing your own date format. We’ll look at some of the up- and downsides of how Swift decodes dates, and how we can possibly work around...

When Swift 2.0 added the throws keyword to the language, folks were somewhat divided on its usefulness. Some people preferred designing their APIs with an (at the time) unofficial implementation of the Result type because that worked with both regular and callback based functions. However, the language feature got adopted and a new complaint came up regularly. The way throws in Swift was designed didn’t allow developers to specify the types of errors that a function could throw. In every do {} catch {} block we write we have to assume and account for any object that conforms to the...

Swift’s current concurrency model leverages tasks to encapsulate the asynchronous work that you’d like to perform. I wrote about the different kinds of tasks we have in Swift in the past. You can take a look at that post here. In this post, I’d like to explore the rules that Swift applies when it determines where your tasks and functions run. More specifically, I’d like to explore how we can determine whether a task or function will run on the main actor or not. We’ll start this post by very briefly looking at tasks and how we can determine where...

With iOS 17, we’ve gained a new way to provide observable data to our SwiftUI views. Until iOS 17, we’d use either an ObservableObject with @StateObject, @ObservedObject, or @EnvironmentObject whenever we had a reference type that we wanted to observe in one of our SwiftUI views. For lots of apps this worked absolutely fine, but these objects have a dependency on the Combine framework (which in my opinion isn’t a big deal), and they made it really hard for developers to limit which properties a view would observe. In iOS 17, we gained the new @Observable macro. I wrote about...