ios-standards

iOS Standards

Swift 6.0+ patterns, strict concurrency, and modern SwiftUI architecture. Apply these patterns to all iOS code.

☠️ ULTIMATE RULE

NEVER KEEP MULTIPLE VERSIONS OF A FEATURE IN CODE (v2Enabled, legacyMode, newFlow, etc.). When replacing a feature, replace it. Delete the old path. Systematic modular variants (enum injection, DI, strategy protocols) are allowed; inline boolean forks are forbidden.

---

☠️ FIT THE PRIMITIVE TO THE PROBLEM

Match the tool to the problem's actual shape, not to an elegant invariant. Before adopting a powerful or opaque Apple framework (CloudKit sharing/CKShare, NSPersistentCloudKitContainer mirroring, NSFileCoordinator, App Intents graphs, widget timelines), name the one job it exists for and confirm your problem needs exactly that. Don't buy a property you want — privacy, safety — that ordinary app logic keeps for free with a heavyweight, unobservable mechanism. Prefer the simplest primitive that ships, is debuggable in production, and fails legibly.

Wrong-primitive signal: you keep fighting a framework's opaque internals and each fix surfaces a new break elsewhere. That is not "one more fix" — it is the platform refusing the wrong primitive. Stop and question the foundation. (Real case: CKShare bent to deliver append-only one-way messages → three weeks of NSCocoaError 134406 wedges; the fix was the right primitive, an encrypted public-DB mailbox — not a better share path.)

Run /fit-check (skill architecture-fit-check) before committing to any such framework.

---

Swift 6 Concurrency

@MainActor Isolation

All UI-related code must be @MainActor isolated.

// WRONG — not MainActor isolated
class TimerViewModel: ObservableObject {
    @Published var timeRemaining: TimeInterval = 0
}

// RIGHT — @MainActor isolated
@MainActor
@Observable
class TimerViewModel {
    var timeRemaining: TimeInterval = 0
}

Common Patterns

// ViewModels — always @MainActor
@MainActor
@Observable
class MyViewModel {
    var state: AppState = .idle
    
    func updateUI() {
        // Safe to touch UI state
    }
}

// Services that touch UI — @MainActor
@MainActor
final class NotificationService {
    func showNotification() {
        // UIKit calls require MainActor
    }
}

// Services that don't touch UI — no annotation needed
final class AnalyticsService {
    func track(event: String) async {
        // Background-safe work
    }
}