anastasiyaw/codex-claude-code-config/ios-development

if #available(iOS 17, *) {
    // SwiftData or @Observable
} else {
    // fallback
}

// Prefer this
func loadUser() async throws -> User {
    let data = try await URLSession.shared.data(from: url).0
    return try JSONDecoder().decode(User.self, from: data)
}
 
// Call site
Task {
    do {
        user = try await loadUser()
    } catch {
        errorMessage = error.localizedDescription
    }
}

enum AppError: LocalizedError {
    case networkUnavailable
    case decodingFailed(String)
    case unauthorized
    
    var errorDescription: String? {
        switch self {
        case .networkUnavailable: return "No internet connection"
        case .decodingFailed(let detail): return "Data error: \(detail)"
        case .unauthorized: return "Please sign in again"
        }
    }
}

Is the screen purely data-display with simple interaction?
  YES → MVC / simple SwiftUI View with @State is fine
  NO ↓
 
Is business logic testable without UI?
  Required → use ViewModel (MVVM) or Store (TCA)
 
Is navigation/routing complex (deep links, coordinator)?
  YES → read references/navigation.md → Coordinator pattern
 
Is the team large or is this a long-lived product?
  YES → Clean Architecture or TCA → read references/architecture.md
 
Default for most apps: MVVM + Coordinator

Local transient state       → @State
Passed from parent          → @Binding
Shared across views         → @StateObject / @ObservedObject (iOS 16-)
                            → @State with @Observable class (iOS 17+)
App-wide environment        → @EnvironmentObject / @Environment

@Observable
class UserStore {
    var users: [User] = []
    var isLoading = false
}
 
// In View — no property wrapper needed
struct UserListView: View {
    var store: UserStore  // just pass it
    var body: some View {
        List(store.users) { Text($0.name) }
    }
}

class UserViewModel: ObservableObject {
    @Published var users: [User] = []
    @Published var isLoading = false
}
 
struct UserListView: View {
    @StateObject private var vm = UserViewModel()
}

// Unit test — ViewModel
@MainActor
final class UserViewModelTests: XCTestCase {
    func testLoadUsers() async throws {
        let vm = UserViewModel(service: MockUserService())
        await vm.loadUsers()
        XCTAssertFalse(vm.users.isEmpty)
    }
}
 
// UI test — basic
func testLoginFlow() {
    let app = XCUIApplication()
    app.launch()
    app.textFields["Email"].tap()
    app.textFields["Email"].typeText("test@example.com")
    app.buttons["Continue"].tap()
    XCTAssertTrue(app.navigationBars["Home"].exists)
}