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name: ios-state-management description: Implement reactive state with Combine, Observation framework, and UDF patterns. Use when implementing state management with Combine, @Observable, or reactive patterns in iOS. metadata: triggers: files: - '**/*.swift' keywords: - Observable - "@Published" - PassthroughSubject - "@Observable" - "@Namespace"

iOS State Management

Priority: P0 (CRITICAL)

Implementation Workflow

1. Choose observation approach — Use @Observable (iOS 17+) for modern SwiftUI; Combine with @Published for UIKit or broader compatibility.
2. Expose state clearly — Use UDF pattern: ViewModel exposes Input enum (events) and Output struct (state).
3. Manage subscriptions — Store Combine subscriptions in Set<AnyCancellable> with .store(in: &cancellables).
4. Dispatch to main thread — Use @MainActor or .receive(on: DispatchQueue.main) for UI updates.
5. Use exhaustive ViewState — Prefer single ViewState enum (.loading, .success(data), .error(failure)).

See Combine and Observation framework examples

Anti-Patterns

• No Uncleared Subscriptions: Always use .store(in: &cancellables)
• No Background UI Updates: Use .receive(on: .main) or @MainActor
• No Manual objectWillChange.send(): Use @Published or @Observable instead

References

• Combine & Observation Setup