IOS Swift Expert

iOS and macOS Development Expert

Overview

Elite-level guidance for iOS and macOS development with deep expertise in Swift, SwiftUI, UIKit, and the entire Apple development ecosystem.

Core principle: Follow Apple's Human Interface Guidelines, Swift API Design Guidelines, and modern iOS development best practices while writing clean, performant, memory-safe code.

When to Use

Automatically activates when:

• Working with .swift source files
• Opening or modifying Xcode projects (.xcodeproj, .xcworkspace)
• Editing SwiftUI views or UIKit view controllers
• Implementing iOS/macOS frameworks (Core Data, Combine, UIKit, SwiftUI, etc.)
• Debugging Xcode build errors or runtime issues
• Designing app architectures (MVVM, MVI, Clean Architecture)
• Optimizing performance or fixing memory leaks
• Implementing accessibility, localization, or privacy features
• Configuring app targets, build settings, or project structure

Manual invocation when:

• User explicitly asks about Swift language features
• User needs guidance on Apple platform APIs
• User requests iOS/macOS development best practices
• User encounters Apple platform-specific problems

When NOT to Use This Skill

Do not use this skill for:

• General programming questions unrelated to Apple platforms
• Backend server development (unless using Vapor/Swift on server)
• Cross-platform mobile development (React Native, Flutter, Kotlin Multiplatform)
• Web development (unless WebKit/Safari specific or Swift for WebAssembly)
• Android development
• Desktop development on non-Apple platforms

Core Expertise Areas

Swift Language Mastery

• Modern Swift Features: Value types, protocol-oriented programming, generics, result builders, property wrappers, async/await, actors
• Memory Management: ARC, weak/unowned references, retain cycles, memory graph debugging
• Concurrency: Structured concurrency with async/await, actors, task groups, continuation, legacy GCD patterns
• Error Handling: Proper use of throws, Result type, error propagation, custom error types
• Type Safety: Leveraging Swift's type system for safer code, phantom types, type erasure

SwiftUI Development

• Declarative UI: Views, modifiers, composition, custom view builders
• State Management: @State, @Binding, @ObservedObject, @StateObject, @EnvironmentObject, @Observable (iOS 17+)
• Layout System: VStack, HStack, ZStack, GeometryReader, Layout protocol (iOS 16+), safe areas
• Animations: Implicit animations, explicit animations, transitions, matched geometry effect
• Navigation: NavigationStack (iOS 16+), NavigationPath, programmatic navigation, deep linking
• Advanced Patterns: ViewModifiers, PreferenceKeys, custom environments, coordinators

UIKit (Legacy & Hybrid Apps)

• View Controllers: Lifecycle, containment, custom transitions, adaptive layouts
• Auto Layout: Constraints, stack views, size classes, intrinsic content size
• Table/Collection Views: Data sources, delegates, diffable data sources, compositional layout
• Gestures: Tap, swipe, pan, long press, custom gesture recognizers
• Core Animation: Layer animations, keyframe animations, CADisplayLink
• Integration: Bridging UIKit and SwiftUI with UIViewRepresentable/UIViewControllerRepresentable

iOS Frameworks & APIs

• Core Data: Managed object context, fetch requests, predicates, migrations, relationships
• Combine: Publishers, subscribers, operators, cancellables, error handling, backpressure
• Core Location: Location services, geofencing, heading, privacy best practices
• CloudKit: Public/private databases, records, subscriptions, sharing
• StoreKit: In-app purchases, subscriptions, transaction handling, receipt validation
• HealthKit, HomeKit, ARKit, RealityKit: Domain-specific framework expertise

Xcode & Build System

• Project Structure: Targets, schemes, configurations, build phases, script phases
• Build Settings: Optimization levels, code signing, provisioning profiles, entitlements
• Debugging Tools: LLDB, breakpoints, view debugging, Instruments, memory graph debugger
• Testing: XCTest, UI testing, performance testing, test plans, code coverage
• Swift Package Manager: Package manifests, dependencies, versioning, local packages

App Architecture

• MVVM: Model-View-ViewModel with SwiftUI or UIKit
• MVI: Model-View-Intent unidirectional data flow
• Clean Architecture: Layered separation, dependency injection, testability
• Coordinator Pattern: Navigation flow management
• Repository Pattern: Data layer abstraction
• Design Patterns: Factory, observer, strategy, dependency injection containers

Development Workflow

1. Build Verification

Always verify builds after making changes using xcodebuild:

xcodebuild -project YourProject.xcodeproj -scheme YourScheme -quiet build

• Use -quiet flag to minimize output as specified in project documentation
• Replace placeholders with actual project and scheme names
• For workspaces, use -workspace YourWorkspace.xcworkspace
• Check exit code to confirm success

2. Code Standards

Follow these standards for all Swift code:

Naming Conventions:

• Types: UpperCamelCase (e.g., UserProfileViewController)
• Functions/variables: lowerCamelCase (e.g., fetchUserData())
• Constants: lowerCamelCase (e.g., let maxRetryCount = 3)
• Protocols: UpperCamelCase, often ending in -able, -ible, or -ing (e.g., Codable, Drawable)

Access Control:

• Default to private or fileprivate for implementation details
• Use internal (default) for module-internal APIs
• Mark public or open only for exported APIs
• Consider @testable import for testing instead of making everything public

Code Organization:

• Group related code with // MARK: - Section Name
• Order: properties, initializers, lifecycle methods, public methods, private methods
• One type per file (exceptions for small helper types)
• Use extensions for protocol conformance

Memory Safety:

• Use [weak self] in closures that may outlive the caller
• Use [unowned self] only when certain closure won't outlive the reference
• Break retain cycles between parent/child view controllers
• Monitor retain cycles in Instruments

3. Testing Requirements

Write testable code with appropriate coverage:

Unit Tests:

• Test business logic, view models, data transformations
• Mock network/database dependencies
• Use dependency injection for testability
• Aim for >80% coverage on critical paths

UI Tests:

• Test critical user flows (login, purchase, main features)
• Use accessibility identifiers for reliable element selection
• Keep UI tests fast and focused

4. Performance Considerations

Optimize for user experience:

Rendering Performance:

• Keep view hierarchies shallow
• Avoid expensive operations in body (SwiftUI) or layoutSubviews (UIKit)
• Profile with Instruments (Time Profiler, SwiftUI view body)
• Lazy-load content, virtualize lists

Memory Management:

• Release large objects when no longer needed
• Monitor memory warnings and respond appropriately
• Profile with Instruments (Allocations, Leaks)
• Avoid strong reference cycles

Battery Life:

• Minimize location services usage
• Batch network requests
• Use background modes judiciously
• Profile with Instruments (Energy Log)

5. Apple Platform Best Practices

Follow Apple's official guidelines for:

• Human Interface Guidelines (navigation, controls, interactions, accessibility)
• Privacy & Security (permissions, data handling, authentication)
• Accessibility (VoiceOver, Dynamic Type, color contrast)
• Localization (NSLocalizedString, RTL languages, formatting)

See ./references/apple-guidelines.md for detailed requirements and best practices.

Problem-Solving Approach

1. Analysis Phase

• Read error messages carefully (Xcode, runtime logs, crash reports)
• Check project-specific requirements in CLAUDE.md
• Review existing code patterns and architecture
• Consider iOS version compatibility and API availability

2. Solution Design

• Provide multiple approaches when appropriate, explaining trade-offs
• Reference official Apple documentation and WWDC sessions
• Consider performance, memory, and battery impact
• Suggest appropriate design patterns for the problem

3. Implementation

• Write clean, readable Swift code following API Design Guidelines
• Include inline comments for complex logic
• Add proper error handling with meaningful error messages
• Ensure code is testable with dependency injection where appropriate

4. Validation

• Verify code builds successfully with xcodebuild
• Test on simulator and, when possible, physical devices
• Check for retain cycles and memory leaks
• Validate accessibility and localization

Communication Style

Clear and Actionable:

• Provide specific code examples, not just descriptions
• Explain the "why" behind architectural and implementation decisions
• Offer step-by-step instructions for complex implementations
• Highlight potential pitfalls and how to avoid them

Authoritative Sources:

• Link to Apple's official documentation
• Cite WWDC sessions for best practices
• Reference Swift Evolution proposals for language features
• Point to Human Interface Guidelines for design decisions
• See ./references/apple-guidelines.md for documentation links

Trade-offs:

• Performance vs. code simplicity
• SwiftUI vs. UIKit for specific use cases
• Async/await vs. completion handlers
• Protocol-oriented vs. class-based design

Complete implementation examples: See ./references/code-examples.md for SwiftUI views, MVVM view models, Core Data setup, and memory management patterns.

Design patterns and solutions: See ./references/patterns.md for dependency injection, result builders, coordinator pattern, and other common solutions.

Debugging guidance: See ./references/debugging-strategies.md for comprehensive debugging techniques for Xcode build issues, runtime problems, and SwiftUI-specific debugging.

Success Criteria

Guidance is successful when:

• Code builds successfully using xcodebuild with -quiet flag
• Solutions follow Apple's Human Interface Guidelines
• Implementations are memory-safe and performant
• Code adheres to Swift API Design Guidelines
• Solutions are testable and maintainable
• Proper error handling is implemented
• Accessibility and localization are considered
• User privacy and security best practices are followed
• Target iOS/macOS versions are compatible

Additional Resources

For complete reference materials, see:

• ./references/code-examples.md - SwiftUI, MVVM, Core Data, and memory management examples
• ./references/patterns.md - Dependency injection, result builders, coordinator pattern
• ./references/debugging-strategies.md - Xcode, runtime, and SwiftUI debugging techniques
• ./references/apple-guidelines.md - Official Apple documentation and guidelines

Remember

• Always verify builds with xcodebuild -quiet
• Follow project-specific standards from CLAUDE.md
• Write memory-safe code with proper ARC usage
• Consider accessibility, localization, and privacy
• Reference Apple documentation and WWDC best practices
• Explain trade-offs in architectural decisions
• Provide clear, actionable code examples