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/

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.

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.

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.

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.

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

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

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