ABOUTME: Apple platform guide - Swift 6, SwiftUI, concurrency, testing, performance

ABOUTME: Modern Swift (2025-2026): @Observable, SwiftData, NavigationStack, strict concurrency

Apple Platform Development

Quick Reference

# Build
xcodebuild -scheme MyApp -sdk iphoneos build
xcodebuild -scheme MyApp -sdk macosx build

# Tests
xcodebuild test -scheme MyApp -destination 'platform=iOS Simulator,name=iPhone 16'

# SwiftLint / SPM
swiftlint lint [--fix]
swift build && swift test && swift package resolve

# ast-grep
sg --pattern '@Observable final class $NAME { $$$ }' --lang swift
sg --pattern '@MainActor' --lang swift

See also: _AST_GREP.md, _PATTERNS.md, source-control, references/

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Swift 6

• Strict concurrency - Data-race safety at compile time
• @Observable - Replaces ObservableObject
• @MainActor - UI thread isolation
• Sendable - Safe cross-actor value types
• Macros - @Observable, @Model, #Preview

Migration: Enable swiftLanguageModes: [.v6], replace ObservableObject, add @MainActor to UI classes, add Sendable to value types, use actors for shared state, replace callbacks with async throws.

For detailed migration patterns, see references/swift6-patterns.md.

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SwiftUI

Property Wrappers

| Wrapper | Use | |---------|-----| | @State | View-owned values, @Observable | | @Binding | Two-way to parent | | @Bindable | Two-way to @Observable props | | @Environment | System/app values | | @StateObject | View-owned ObservableObject (legacy) |

View property order: @Environment, let, @State/@Binding, computed, init, body, private methods

View sizing: <100 lines = single view; 100-200 = extract subviews; >200 = multiple files; business logic = @Observable VM; network/DB = repository pattern

For NavigationStack, SwiftData, MVVM, and DI patterns, see references/swiftui-patterns.md.

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Concurrency

Common Fixes

| Error | Fix | |-------|-----| | Main actor isolation | Add @MainActor to class/func | | Non-isolated access | Mark nonisolated | | Sendable violation | Add @unchecked Sendable or fix | | Protocol async | Require async in protocol | | Closure capture | Use @Sendable closure |

When to use what

| Use Case | Choice | |----------|--------| | One-shot network | async/await | | Parallel fetches | async let / TaskGroup | | Real-time streams | Combine / AsyncStream | | UI events, debounce | Combine |

For MainActor, parallel execution, and actor patterns, see references/concurrency-patterns.md.

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Architecture

MVVM with @Observable: @Observable @MainActor final class VM with private(set) properties, injected service protocols, async load methods with defer { isLoading = false }.

DI: Protocol-based with EnvironmentKey for SwiftUI injection.

Testing (Swift Testing, iOS 18+): @Suite, @Test, #expect. Parameterized with arguments:. Mock via protocol injection.

For full code examples, see references/swiftui-patterns.md and references/swift6-patterns.md.

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Review Checklists

Concurrency: MainActor for UI, Sendable for cross-actor data, task cancellation handled, no data races (Swift 6)

SwiftUI: @Observable not ObservableObject (iOS 17+), NavigationStack not NavigationView, .task not .onAppear + Task, LazyVStack for long lists

CRITICAL: Force unwrap without safety, UI updates off MainActor, data races, retain cycles

HIGH: ObservableObject when @Observable available, NavigationView instead of NavigationStack

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Detailed References

• references/swift6-patterns.md - Swift 6 migration, Sendable, actors, macros
• references/swiftui-patterns.md - NavigationStack, SwiftData, MVVM, dependency injection
• references/concurrency-patterns.md - async/await, TaskGroup, MainActor, actors, AsyncStream
• references/performance.md - Optimization, Instruments profiling, memory management

Official: Swift | SwiftUI | SwiftData

Libraries: TCA | Snapshot Testing | SwiftLint