Migrating to 1.16

The .appStorage strategy used with @Shared now uses key-value observing instead of NotificationCenter when possible. Learn how this may affect your code.

Overview

There are no steps needed to migrate to 1.16 of the Composable Architecture, but there has been a change to the underlying behavior of .appStorage that one should be aware of. When using .appStorage with @Shared, if your key does not contain the characters "." or "@", then changes to that key in UserDefaults will be observed using key-value observing (KVO). Otherwise, NotificationCenter will be used to observe changes.

KVO is a far more efficient way of observing changes to UserDefaults and it works cross-process, such as from widgets and app extensions. However, KVO does not work when the keys contain "." or "@", and so in those cases we must use the cruder tool of NotificationCenter. That is not as efficient, and it forces us to perform a thread-hop when the notification is posted before we can update the @Shared value. For this reason it is not possible to animate changes that are made directly to UserDefaults:

withAnimation {
  // ⚠️ This will not animate any SwiftUI views using '@Shared(.appStorage("co.pointfree.count"))'
  UserDefaults.standard.set(0, forKey: "co.pointfree.count")
}

In general, we recommend using other delimeters for your keys, such as "/", ":", "-", etc.:

@Shared(.appStorage("co:pointfree:count")) var count = 0