swift

Swift

Model the domain with types; concur with async/await and isolation. UI: swiftui-development. Persistence: swiftdata. Tests: swift-testing. Server: vapor-swift.

Tooling

• Swift 6 / concurrency checking in new code if the target allows it; respect the app's deployment.
• SwiftPM or Xcode project — preserve the repo's.
• swift-format / SwiftLint if they already exist.

Organization

Sources/MyAppCore/
  Models/
  Services/
Tests/MyAppCoreTests/

• Modules by boundary (MyAppCore vs MyAppUI).
• internal default; public/package only stable API.
• Avoid *Kit dumping ground.

Language

• struct / enum for values; class / actor when there is identity or isolation.
• enum associated for closed states. switch exhaustive.
• let default. Explicit mutation (mutating, var local).
• Domain property wrappers (@Clamped) only with a clear API.
• Generics with real constraints; some/any aware (any Error vs typed).
• Sendable on data that crosses isolation; not @unchecked Sendable without an invariant.

struct UserID: Hashable, Sendable {
    var raw: String
}

enum LoadState<Value: Sendable>: Sendable {
    case loading
    case ready(Value)
    case failed(String)
}

Errors

• throws / Result at the edge. LocalizedError for UI.
• Do not try! on input/I/O. fatalError only for a programming invariant.
• Typed errors (enum AuthError) in libs; do not NSError new.

Concurrency

• async/await to the edge. Task with cancellation (Task.isCancelled / withTaskCancellationHandler).
• actor for shared mutable state. UI: Isolation MainActor in view model APIs.
• Avoid DispatchQueue loose in new code if Task solves it.
• Data races: handle Swift 6 warnings; do not silence with @preconcurrency broad.
• UI detail: swiftui-development. Thread-safe persistence: swiftdata.

Interop

• Bridging NS* only at Objective-C edges.
• nonisolated on Sendable types that do not touch UIKit/AppKit.

Anti-patterns

• AnyObject + KVO in new code
• Assume View / SwiftUI in this skill
• shared mutable singleton without an actor
• Force unwrap on JSON/network
• Task.detached to “fix” the compiler

Integration with other skills

• SwiftUI: swiftui-development
• macOS: macos-development
• watchOS: watchos-development
• SwiftData: swiftdata
• StoreKit: storekit
• Widgets: widgetkit
• Tests: swift-testing
• MVVM: mvvm-architecture

Completion criteria

• Clear Sendable types/sealed states
• async with cancellation at the edges
• No try! / force unwrap in I/O
• Honest isolation (MainActor vs domain actor)
• Tests for the touched core