sjungling/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

Broad expertise across the Apple development ecosystem: Swift language, SwiftUI, UIKit, all major Apple frameworks (Core Data, Combine, CloudKit, StoreKit, HealthKit, ARKit, etc.), Xcode build system, and app architecture patterns (MVVM, MVI, Clean Architecture, Coordinator).

Decision Frameworks

SwiftUI vs UIKit:

• Prefer SwiftUI for new views; use UIKit only for legacy code or unavailable SwiftUI APIs
• Use UIViewRepresentable to bridge UIKit, not the reverse

State Management:

• @State: local value types
• @StateObject: reference types created by the view
• @EnvironmentObject: dependency injection across hierarchy
• @Observable (iOS 17+): preferred for new code

Concurrency:

• Use async/await, not completion handlers
• Use actors for shared mutable state
• Use MainActor for UI updates
• Use TaskGroup for parallel work

Data Persistence:

• SwiftData (iOS 17+): preferred for new projects
• Core Data: existing projects or compatibility needs
• Keychain: credentials and sensitive data only

Architecture:

• MVVM: default for SwiftUI
• Clean Architecture: multi-team projects with heavy testing

Development Workflow

1. Build Verification

Verify builds using xcodebuild -project <project> -scheme <scheme> build or -workspace for multi-target projects. Use the -quiet flag to suppress verbose output. Check exit code to confirm success.

2. Code Standards

Follow Swift API Design Guidelines. Key conventions:

• UpperCamelCase for types, lowerCamelCase for functions/variables
• Default to private; only expose what's needed
• Use // MARK: - to organize: properties, init, lifecycle, public, private
• Use [weak self] in escaping closures; break retain cycles between parent/child

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)

Performance Profiling:

Use xctrace to capture Instruments traces from CLI: xctrace record --template 'Time Profiler' --attach <pid> --output trace.trace --time-limit 10s. Key templates: Time Profiler (CPU), Allocations (memory), SwiftUI (view renders), Animation Hitches (frame drops).

See ./references/debugging-strategies.md for detailed profiling workflows and analysis patterns.

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.

Common Mistakes

| Mistake | Fix | |---------|-----| | Force-unwrapping optionals | Use guard let, if let, or ?? | | Expensive work in SwiftUI body | Move to .task {} or ViewModel | | Missing [weak self] in escaping closures | Always use [weak self] to break cycles | | Synchronous network on main thread | Use async/await | | Hard-coded UI strings | Use String(localized:) for L10n |

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