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Builds iOS/macOS/watchOS/tvOS applications, implements SwiftUI views and state management, designs protocol-oriented architectures, handles async/await concurrency, implements actors for thread safety
The skill file stays in the publisher's repository.
Paste the copied command in a terminal. It installs this SKILL.md into that agent.
npx skills add Jeffallan/claude-skills --skill swift-expert -a cursor -y
Builds iOS/macOS/watchOS/tvOS applications, implements SwiftUI views and state management, designs protocol-oriented architectures, handles async/await concurrency, implements actors for thread safety, and debugs Swift-specific issues. Use when building iOS/macOS applications with Swift 5.9+, SwiftUI, or async/await concurrency. Invoke for protocol-oriented programming, SwiftUI state management, actors, server-side Swift, UIKit integration, Combine, or Vapor.
Builds iOS/macOS/watchOS/tvOS applications, implements SwiftUI views and state management, designs protocol-oriented architectures, handles async/await concurrency, implements actors for thread safety, and debugs Swift-specific issues. Use when building iOS/macOS applications with Swift 5.9+, SwiftUI, or async/await concurrency. Invoke for protocol-oriented programming, SwiftUI state management, actors, server-side Swift, UIKit integration, Combine, or Vapor.
Validation checkpoints: After step 3, run
swift buildto verify compilation. After step 4, runswift build -warnings-as-errorsto surface actor isolation and Sendable warnings. After step 5, runswift testand confirm all async tests pass.
Load detailed guidance based on context:
| Topic | Reference | Load When |
|---|---|---|
| SwiftUI | references/swiftui-patterns.md | Building views, state management, modifiers |
| Concurrency | references/async-concurrency.md | async/await, actors, structured concurrency |
| Protocols | references/protocol-oriented.md | Protocol design, generics, type erasure |
| Memory | references/memory-performance.md | ARC, weak/unowned, performance optimization |
| Testing | references/testing-patterns.md | XCTest, async tests, mocking strategies |
// ✅ DO: async/await with structured error handling
func fetchUser(id: String) async throws -> User {
let url = URL(string: "https://api.example.com/users/\(id)")!
let (data, _) = try await URLSession.shared.data(from: url)
return try JSONDecoder().decode(User.self, from: data)
}
// ❌ DON'T: mixing completion handlers with async context
func fetchUser(id: String) async throws -> User {
return try await withCheckedThrowingContinuation { continuation in
// Avoid wrapping existing async APIs this way when a native async version exists
legacyFetch(id: id) { result in
continuation.resume(with: result)
}
}
}
// ✅ DO: use @Observable (Swift 5.9+) for view models
@Observable
final class CounterViewModel {
var count = 0
func increment() { count += 1 }
}
struct CounterView: View {
@State private var vm = CounterViewModel()
var body: some View {
VStack {
Text("\(vm.count)")
Button("Increment", action: vm.increment)
}
}
}
// ❌ DON'T: reach for ObservableObject/Published when @Observable suffices
class LegacyViewModel: ObservableObject {
@Published var count = 0 // Unnecessary boilerplate in Swift 5.9+
}
// ✅ DO: define capability protocols with associated types
protocol Repository<Entity> {
associatedtype Entity: Identifiable
func fetch(id: Entity.ID) async throws -> Entity
func save(_ entity: Entity) async throws
}
struct UserRepository: Repository {
typealias Entity = User
func fetch(id: UUID) async throws -> User { /* … */ }
func save(_ user: User) async throws { /* … */ }
}
// ❌ DON'T: use classes as base types when a protocol fits
class BaseRepository { // Avoid class inheritance for shared behavior
func fetch(id: UUID) async throws -> Any { fatalError("Override required") }
}
// ✅ DO: isolate mutable shared state in an actor
actor ImageCache {
private var cache: [URL: UIImage] = [:]
func image(for url: URL) -> UIImage? { cache[url] }
func store(_ image: UIImage, for url: URL) { cache[url] = image }
}
// ❌ DON'T: use a class with manual locking
class UnsafeImageCache {
private var cache: [URL: UIImage] = [:]
private let lock = NSLock() // Error-prone; prefer actor isolation
func image(for url: URL) -> UIImage? {
lock.lock(); defer { lock.unlock() }
return cache[url]
}
}
async/await for asynchronous operations (see pattern above)Sendable compliance for concurrencystruct/enum) by default/// …)!) without justificationWhen implementing Swift features, provide:
Maintained by @jeffallan, Principal Consultant at Synergetic Solutions