anti-patterns

Anti-patterns and Common Mistakes to Avoid

Singleton Anti-patterns

❌ NEVER: Static Shared Instances Without Dependency Injection (.shared instance pattern)

Example: See singleton-antipattern.swift

❌ NEVER: Global State Access

// ❌ AVOID - Global state access
var globalSettings: [String: Any] = [:]

func someFunction() {
    globalSettings["key"] = "value" // Global state is hard to test and debug
}

// ✅ CORRECT - Injected dependencies
final class SomeService {
    private let settings: AppSettings
    
    init(settings: AppSettings) {
        self.settings = settings
    }
    
    func someFunction() {
        settings.setValue("value", for: "key")
    }
}

Async/Await Anti-patterns

❌ NEVER: UI Updates Without @MainActor

Example: See async-ui-updates.swift

❌ NEVER: Unhandled Async Errors

// ❌ AVOID - Swallowing async errors
func fetchData() async {
    let data = try? await networkService.getData() // Silently ignoring errors
    // Process data...
}

// ✅ CORRECT - Proper error handling
func fetchData() async throws {
    let data = try await networkService.getData()
    // Process data...
}

// Or handle errors appropriately:
func fetchData() async {
    do {
        let data = try await networkService.getData()
        // Process data...
    } catch {
        // Log error and show user-friendly message
        logger.error("Failed to fetch data: \(error)")
        await showError(error)
    }
}

❌ NEVER: Blocking Main Thread with Sync Operations

// ❌ AVOID - Blocking main thread
@MainActor
func loadData() {
    let data = NetworkService.fetchDataSynchronously() // Blocks UI
    updateUI(with: data)
}

// ✅ CORRECT - Use async operations
@MainActor
func loadData() async {
    let data = try await NetworkService.fetchData() // Non-blocking
    updateUI(with: data)
}

Memory Management Anti-patterns