You may have noticed that the Swift compiler automatically treats the closure of a DispatchQueue.main.async call as @MainActor. In other words, we can call a main-actor-isolated function in the closure: import Dispatch @MainActor func mainActorFunc() { } DispatchQueue.main.async { // The compiler lets us call this because // it knows we’re on the main actor.…
The Swift website provides nightly builds of the Swift compiler (called toolchains) for download. Building with a nightly compiler can be useful if you want to check if a bug has already been fixed on main, or if you want to experiment with upcoming language features such as Embedded Swift, as I’ve been doing lately.…
Git famously doesn’t track file renames. That is, Git doesn’t store the information “file A has been renamed to B in commit X”. Instead, Git stores snapshots of the repository at each commit. It then uses a (customizable) heuristic during diffing to guess at likely renames: “File B in commit X is new, and file…
After my previous post Tracking renamed files in Git, here’s another entry in my ongoing series “I thought git mv was useless but I was wrong”. This one’s especially relevant to users on macOS and Windows, where the file system is case-insensitive by default. More precisely, APFS on macOS is case-insensitive but case-preserving by default.…
We released the fifth edition of our book Advanced Swift a few days ago. You can buy the ebook on the objc.io site. The hardcover print edition is printed and sold by Amazon (amazon.com, amazon.co.uk, amazon.de). Highlights of the new edition: Fully updated for Swift 5.6 A new Concurrency chapter covering async/await, structured concurrency, and…
The environment in SwiftUI is sort of like a global dictionary but with stronger types: each key (represented by a key path) can have its own specific value type. For example, the .isEnabled key stores a boolean value, whereas the .font key stores an Optional<Font>. I wrote a custom dictionary type that can do the…
Here’s a simple AttributedString with some formatting: import Foundation let str = try! AttributedString( markdown: “Café **Sol**”, options: .init(interpretedSyntax: .inlineOnly) ) AttributedString is Codable. If your task was to design the encoding format for an attributed string, what would you come up with? Something like this seems reasonable (in JSON with comments): { “text”: “Café…
@MainActor is a Swift annotation to coerce a function to always run on the main thread and to enable the compiler to verify this. How does this work? In this article, I’m going to reimplement @MainActor in a slightly simplified form for illustration purposes, mainly to show how little “magic” there is to it. The…
iOS 16 beta 4 is the first SDK release that supports Live Activities. A Live Activity is a widget-like view an app can place on your lock screen and update in real time. Examples where this can be useful include live sports scores or train departure times. These are my notes on playing with the…
SwiftUI’s .task modifier inherits its actor context from the surrounding function. If you call .task inside a view’s body property, the async operation will run on the main actor because View.body is (semi-secretly) annotated with @MainActor. However, if you call .task from a helper property or function that isn’t @MainActor-annotated, the async operation will run…