ios-architecture

iOS DuckDuckGo Browser Architecture Rules

Dependency Injection and AppDependencies

Use AppDependencyProvider Pattern

ALWAYS use the centralized dependency provider for all service dependencies:

// ✅ CORRECT - Use the shared dependency provider
final class FeatureViewModel: ObservableObject {
    private let networkService: NetworkServiceProtocol
    
    init(dependencies: DependencyProvider = AppDependencyProvider.shared) {
        self.networkService = dependencies.networkService
    }
}

// ❌ INCORRECT - Direct singleton access
final class FeatureViewModel: ObservableObject {
    private let networkService = NetworkService.shared // Avoid singletons
}

Protocol-Based Dependencies

ALWAYS define protocols for dependencies to enable testing:

// ✅ CORRECT - Protocol abstraction
protocol FeatureServiceProtocol {
    func fetchData() async throws -> [Item]
}

final class FeatureService: FeatureServiceProtocol {
    // Implementation
}

// ❌ INCORRECT - Concrete dependency
final class ViewModel {
    private let service: FeatureService // Hard to test
}

AppSettings and Configuration

Use AppSettings Protocol

ALWAYS access settings through the AppSettings protocol:

// ✅ CORRECT - Protocol-based settings access
final class SettingsViewModel: ObservableObject {
    private let appSettings: AppSettings
    
    init(appSettings: AppSettings) {
        self.appSettings = appSettings
    }
    
    var isFeatureEnabled: Bool {
        get { appSettings.featureEnabled }
        set { appSettings.featureEnabled = newValue }
    }
}

// ❌ INCORRECT - Direct UserDefaults access
final class SettingsViewModel: ObservableObject {
    var isFeatureEnabled: Bool {
        get { UserDefaults.standard.bool(forKey: "feature_enabled") }
        set { UserDefaults.standard.set(newValue, forKey: "feature_enabled") }
    }
}

UserDefaults Property Wrapper

Use the established @UserDefaultsWrapper pattern for new settings:

// ✅ CORRECT - Property wrapper usage
extension AppUserDefaults {
    @UserDefaultsWrapper(key: .newFeatureEnabled, defaultValue: false)
    var newFeatureEnabled: Bool
}

// ❌ INCORRECT - Manual UserDefaults handling
extension AppUserDefaults {
    var newFeatureEnabled: Bool {
        get { userDefaults.bool(forKey: "new_feature_enabled") }
        set { userDefaults.set(newValue, forKey: "new_feature_enabled") }
    }
}