# Swift > Swift and iOS development with modern patterns and best practices Use when this capability is needed. - Skill: `tomevault-io/swift-4` (Agent Skill, multi-file: 2 files) - Install (CLI): `npx skillmds@latest add tomevault-io/swift-4` - Raw SKILL.md: https://api.skillmd.com/api/skills/tomevault-io/swift-4/raw - Safety review: pending (external: skill-scanner PASS, skillspector PASS) - Works with: Claude Code, Claude.ai, OpenAI Codex - Category: Coding & Dev Tools - Author: tomevault-io (https://skillmd.com/u/tomevault-io) - Updated: 2026-09-17 - Page: https://skillmd.com/skills/tomevault-io/swift-4 --- # Swift You are a Swift and iOS development expert. Apply these guidelines when working on Swift code. ## Target Requirements - Swift 6+ with modern Swift concurrency - SwiftUI with `@Observable` for shared data - No third-party frameworks without explicit approval - Avoid UIKit unless explicitly requested - Follow Apple Human Interface Guidelines ## Code Organization ### Extension-Based Grouping Organize related functionality using extensions: ```swift // MARK: - Main View struct BooksView: View { @State private var books: [Book] = [] var body: some View { List(books) { book in BookCell(book: book) } } } // MARK: - Subviews extension BooksView { struct BookCell: View { let book: Book var body: some View { HStack { BookCover(url: book.coverURL) BookInfo(book: book) } } } struct BookCover: View { let url: URL? var body: some View { /* ... */ } } struct BookInfo: View { let book: Book var body: some View { /* ... */ } } } // MARK: - View Model extension BooksView { @Observable @MainActor final class ViewModel { var books: [Book] = [] var isLoading = false func loadBooks() async { /* ... */ } } } ``` ### File Structure - Place each struct/class/enum in separate Swift files - Don't break views into computed properties; use separate `View` structs - Organize by feature, not layer ``` Features/ ├── Books/ │ ├── BooksView.swift │ ├── BookDetailView.swift │ └── Models/ ├── Settings/ │ └── SettingsView.swift └── Shared/ ├── Components/ └── Extensions/ ``` ## Naming Conventions ```swift // Types: UpperCamelCase struct UserProfile { } enum NetworkError { } protocol DataFetching { } // Properties and methods: lowerCamelCase var currentUser: User func fetchUserData() async throws -> User // Boolean properties: use assertion form var isEnabled: Bool var hasUnreadMessages: Bool var canSubmit: Bool // Collections: use plural nouns var users: [User] var selectedItems: Set // Mutating vs non-mutating func add(_ item: Item) // mutates func adding(_ item: Item) -> [Item] // returns new ``` ## SwiftUI Patterns ### State Management ```swift // Local UI state only @State private var searchText = "" // Observable objects (iOS 17+) - prefer @Observable over ObservableObject @Observable @MainActor final class ProfileViewModel { var user: User? var isLoading = false } // In views @State private var viewModel = ProfileViewModel() // For passed-in observable objects @Bindable var viewModel: ProfileViewModel ``` ### Modern Modifiers (Use These) ```swift .foregroundStyle(.primary) // NOT foregroundColor() .clipShape(.rect(cornerRadius: 12)) // NOT cornerRadius() .bold() // NOT fontWeight(.bold) .scrollIndicators(.hidden) // to hide scroll bars // Modern Tab API - NOT tabItem() TabView { Tab("Home", systemImage: "house") { HomeView() } Tab("Settings", systemImage: "gear") { SettingsView() } } ``` ### Deprecated Patterns to Avoid ```swift // DON'T use single-parameter onChange .onChange(of: value) { newValue in } // DEPRECATED // DO use two-parameter version .onChange(of: value) { oldValue, newValue in } // For iOS 17+, prefer @Observable over ObservableObject class MyViewModel: ObservableObject { } // Legacy (iOS 13-16) @Observable class MyViewModel { } // Modern (iOS 17+) ``` ### Layout ```swift // DON'T use UIScreen.main.bounds let width = UIScreen.main.bounds.width // BAD // DO use containerRelativeFrame or visualEffect .containerRelativeFrame(.horizontal) { width, _ in width * 0.8 } // Prefer containerRelativeFrame() or visualEffect() over GeometryReader // Use ImageRenderer instead of UIGraphicsImageRenderer let renderer = ImageRenderer(content: myView) if let image = renderer.uiImage { } ``` ### Buttons and Gestures ```swift // DON'T use onTapGesture for buttons Image(systemName: "plus") .onTapGesture { action() } // BAD // DO use Button with labels Button { action() } label: { Label("Add Item", systemImage: "plus") } // Only use onTapGesture when tracking tap location or count ``` ### Navigation ```swift // Modern navigation with type-safe destinations NavigationStack { List(items) { item in NavigationLink(value: item) { ItemRow(item: item) } } .navigationDestination(for: Item.self) { item in ItemDetailView(item: item) } } ``` ### Collections ```swift // DO use enumerated directly ForEach(Array(items.enumerated()), id: \.element.id) { index, item in Text("\(index): \(item.name)") } // DON'T convert to array first unnecessarily ``` ## Modern Swift APIs ### Concurrency ```swift // Modern sleep - NOT Task.sleep(nanoseconds:) try await Task.sleep(for: .seconds(1)) // NEVER use DispatchQueue.main.async() DispatchQueue.main.async { } // BAD // DO use MainActor await MainActor.run { } // or mark with @MainActor // All @Observable classes should be @MainActor @Observable @MainActor final class ViewModel { } ``` ### Modern Foundation ```swift // Directory access let documents = URL.documentsDirectory let cache = URL.cachesDirectory // Path manipulation let file = documents.appending(path: "data.json") // String operations - NOT replacingOccurrences(of:with:) let result = text.replacing("old", with: "new") // Text filtering - NOT contains() items.filter { $0.name.localizedStandardContains(searchText) } ``` ### Text Formatting ```swift // Use format parameter - NOT C-style or NumberFormatter Text(price, format: .currency(code: "USD")) Text(date, format: .dateTime.month().day()) Text(count, format: .number.precision(.fractionLength(2))) ``` ### Static Member Lookup ```swift // Prefer static members over initializers .buttonStyle(.borderedProminent) // NOT BorderedProminentButtonStyle() .clipShape(.capsule) // NOT Capsule() .clipShape(.circle) // NOT Circle() .background(.ultraThinMaterial) ``` ## SwiftUI Colors ```swift // DON'T use UIKit colors in SwiftUI Color(UIColor.systemBackground) // BAD // DO use SwiftUI colors Color(.systemBackground) // OK Color.primary Color.secondary ``` ## Dynamic Type ```swift // DON'T override Dynamic Type .font(.system(size: 16)) // BAD - fixed size // DO respect system font sizing .font(.body) .font(.headline) // Avoid hard-coded padding and spacing values ``` ## SwiftData ### Basic Setup ```swift @Model final class Book { var title: String var author: String var publishedDate: Date var rating: Int? @Relationship(deleteRule: .cascade) var chapters: [Chapter]? init(title: String, author: String, publishedDate: Date) { self.title = title self.author = author self.publishedDate = publishedDate } } ``` ### CloudKit Compatibility When using iCloud sync: - NEVER use `@Attribute(.unique)` - All properties need default values or be optional - Mark ALL relationships as optional ## Error Handling ```swift // Define specific error types enum DataError: LocalizedError { case networkUnavailable case invalidResponse(statusCode: Int) case decodingFailed(underlying: Error) var errorDescription: String? { switch self { case .networkUnavailable: return "Network connection unavailable" case .invalidResponse(let code): return "Server returned error \(code)" case .decodingFailed: return "Failed to process server response" } } } // Avoid force try and force unwrap (except truly unrecoverable cases) do { let data = try await fetchData() let result = try decoder.decode(Response.self, from: data) } catch { logger.error("Failed to load: \(error)") throw DataError.decodingFailed(underlying: error) } ``` ## Testing ### Swift Testing Framework ```swift import Testing struct AuthenticationTests { @Test("User can log in with valid credentials") func successfulLogin() async throws { let auth = AuthService() let result = try await auth.login(email: "test@example.com", password: "valid") #expect(result.isAuthenticated) } @Test("Login fails with wrong password") func failedLogin() async { let auth = AuthService() await #expect(throws: AuthError.invalidCredentials) { try await auth.login(email: "test@example.com", password: "wrong") } } } ``` ### Testing Guidelines - Write unit tests for core application logic - UI tests only when unit tests aren't feasible - Place view logic in view models for testability ## iOS Version Features ### iOS 17+ - `@Observable` macro replaces `ObservableObject` - `@Bindable` for bindings to observable objects - SwiftData for persistence - TipKit for onboarding hints ### iOS 18+ - Enhanced SwiftData with `#Index` and `#Unique` - Control Center widgets - `@Previewable` macro for simpler previews ### iOS 26+ - Liquid Glass design system - New translucent materials - Modern Tab API ## Things to Avoid 1. **Force unwrapping** - Use `if let`, `guard let`, or nil coalescing 2. **AnyView** - Use `@ViewBuilder` or concrete types 3. **GeometryReader** - Try `containerRelativeFrame` first 4. **UIScreen.main.bounds** - Use proper layout APIs 5. **ObservableObject** - Use `@Observable` instead (iOS 17+) 6. **DispatchQueue.main.async** - Use `@MainActor` 7. **Hard-coded sizes** - Respect Dynamic Type 8. **UIKit colors** - Use SwiftUI colors 9. **Computed property views** - Use separate View structs 10. **Single-param onChange** - Use two-parameter version ## Security - NEVER commit secrets, API keys, or configuration data - Use environment variables or secure storage - Follow App Store Review Guidelines ## Before Committing - Run SwiftLint; fix all warnings and errors - Ensure no force unwraps without justification - Verify async code uses proper actors - Check that views support Dynamic Type - Write tests for business logic - Add documentation comments as needed --- > Converted and distributed by [TomeVault](https://tomevault.io/claim/onmyway133) — claim your Tome and manage your conversions.