SwiftUI macro improvements

iOS 18 brought more macro improvements to SwiftUI. The @Observable macro got some nice updates.

One thing that's better - you can now use @Observable with protocols, which wasn't possible before:

@Observable
protocol ViewModel {
    var isLoading: Bool { get set }
    func loadData()
}

class UserViewModel: ViewModel {
    var isLoading: Bool = false
    
    func loadData() {
        isLoading = true
        // Load data
        isLoading = false
    }
}

But here's what I learned - the observation tracking is more efficient now. SwiftUI only updates views when the specific properties they're using change, not when any property changes.

Also, if you're using @Observable with computed properties, make sure they're not doing expensive work. The observation system will track dependencies, but you still need to be careful:

@Observable
class ViewModel {
    var items: [Item] = []
    
    var filteredItems: [Item] {
        items.filter { $0.isActive } // This runs on every access
    }
}

One gotcha - if you need to observe from outside SwiftUI (like in Combine or async contexts), you can use withObservationTracking, but it's still a bit verbose.

And if you're migrating from @ObservableObject, the migration is mostly straightforward, but watch out for @Published properties that were computed. Those need special handling.

The macro system is getting more powerful, but it's still SwiftUI-specific. If you need observation outside SwiftUI, you might still need Combine or manual observation.

Thanks for reading! Check out more posts on the blog if you'd like.