swift-architecture

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Summary

Selects, reviews, and migrates Apple-platform app architectures across MV with Observation, MVVM, MVI, TCA, Clean Architecture, Coordinator, and legacy VIPER. Use when choosing module and dependency boundaries, escalating a feature beyond simple SwiftUI MV, planning incremental architecture migration, or auditing state ownership and test seams.

SKILL.md

Swift Architecture

Choose the smallest architecture that makes state ownership, dependencies, side effects, and tests explicit. Default new SwiftUI features to MV; escalate only for observed complexity.

Scope Boundary
Decision Workflow
Pattern Selection
MV Default
Escalation Signals
Migration
Common Mistakes
Review Checklist
References

Scope Boundary

This skill owns pattern selection, module boundaries, dependency direction, migration strategy, and architecture-level test seams. Route SwiftUI property-wrapper wiring and view composition to swiftui-patterns, navigation APIs and route models to swiftui-navigation, isolation diagnostics to swift-concurrency, and test syntax/fixtures to swift-testing.

Decision Workflow

Record the feature's state owner, inputs, outputs, dependencies, side effects, navigation handoffs, and current tests.
Identify the concrete pressure: complex state machine, shared derived state, dependency control, feature composition, team ownership, or UIKit navigation.
Select the smallest pattern that addresses that pressure; write down what it adds and what remains unchanged.
Implement one vertical slice with injected dependencies and observable state transitions.
Run existing behavior tests plus state-transition and dependency-failure tests. If behavior changes, restore the fixture, fix the smallest boundary, and rerun before migrating another slice.

Pattern	Choose when	Main cost
MV	SwiftUI feature has straightforward state and orchestration	Logic can drift into large views without decomposition
MVVM	Presentation logic needs an independently testable adapter	Extra layer can become a forwarding shell
MVI	A feature is best modeled as explicit state + intents + reducer/effects	Boilerplate and centralized transition design
TCA	Many composable features need deterministic effects, dependencies, and testing	Framework learning and architectural commitment
Clean Architecture	Large product needs strict dependency direction across domain/data/UI	Protocol and mapping overhead
Coordinator	UIKit or hybrid navigation needs a separate flow owner	Another lifecycle and routing owner
VIPER	Maintaining an existing UIKit module with established VIPER boundaries	Very high ceremony; poor default for new SwiftUI work

@MainActor
@Observable
final class TripStore {
    private let client: TripClient
    var trips: [Trip] = []
    var error: Error?

    init(client: TripClient) { self.client = client }

    func load() async {
        do { trips = try await client.fetchTrips() }
        catch { self.error = error }
    }
}

struct TripList: View {
    @State private var store: TripStore

    init(client: TripClient) {
        _store = State(initialValue: TripStore(client: client))
    }

    var body: some View {
        List(store.trips) { Text($0.name) }
            .task { await store.load() }
    }
}

Mistake	Fix
Pattern chosen by popularity	Tie it to an observed feature pressure.
View model only forwards properties	Remove it and use MV.
One object owns navigation, networking, formatting, persistence, and UI state	Split by responsibility and dependency direction.
TCA or Clean Architecture applied to trivial screens	Start with MV and preserve an escalation seam.
Coordinator used as a state architecture	Keep it focused on route/lifecycle ownership.
Multiple patterns mixed inside one feature	Define one local state/effect model and migrate at feature boundaries.
Big-bang migration	Move one tested vertical slice and rerun the same proof matrix.

swift-architecture

Summary

SKILL.md

Swift Architecture

Contents

Scope Boundary

Decision Workflow

Pattern Selection

MV Default

Escalation Signals

Migration

Common Mistakes

Review Checklist

References

Related skills