swift-core

Covers Swift 6 language and platform fundamentals shared across iOS, macOS, iPadOS, watchOS, and visionOS: async/await and actors with strict concurrency checking, Sendable typing, app architecture (MVVM with @Observable as the recommended default, Clean Architecture for complex apps), async testing with XCTest, String Catalog-based localization, and performance profiling with Instruments.

References cover each area in depth: concurrency, architecture/DI, testing, i18n, and performance.

Best practices: prefer actors over classes with locks for shared state, @Observable over ObservableObject, structured concurrency over completion handlers, String Catalogs for all user-facing text, profiling in Release (-O) builds, and value types (structs) over classes where possible.

Swift Core

Swift 6 fundamentals shared across all Apple platforms.

Agent Workflow (MANDATORY)

Before ANY implementation, spawn 3 agents in parallel, one Agent call each with a name:

1. fuse-ai-pilot:explore-codebase - Analyze existing Swift patterns
2. fuse-ai-pilot:research-expert - Verify latest Swift 6 docs via Context7/Exa
3. mcp__apple-docs__search_apple_docs - Check Swift concurrency patterns

After implementation, run fuse-ai-pilot:sniper for validation.

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Overview

When to Use

• Implementing async/await, actors, Sendable
• Designing app architecture (MVVM, Clean Architecture)
• Writing async tests with XCTest
• Localizing with String Catalogs
• Profiling with Instruments

Why Swift Core

Feature	Benefit
Actors	Thread-safe shared state without locks
@Observable	Simple reactive state (replaces ObservableObject)
String Catalogs	Automatic localization with Xcode 15+
Instruments	Built-in performance profiling

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Key Concepts

Concurrency (Swift 6)

Modern async/await with strict concurrency checking. Actors provide thread-safe state, Sendable marks safe types.

Architecture

MVVM with @Observable is the recommended pattern. Clean Architecture for complex apps with domain separation.

Testing

XCTest with native async/await support. No need for expectations with async tests.

Internationalization

String Catalogs are mandatory. All user-facing text must be localized.

Performance

Profile with Instruments. Use lazy loading, avoid heavy work in view body.

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Reference Guide

Need	Reference
Async/await, actors, Sendable	concurrency.md
MVVM, Clean Architecture, DI	architecture.md
XCTest, async tests, mocking	testing.md
String Catalogs, localization	i18n.md
Instruments, optimization	performance.md

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Best Practices

1. Actors for shared state - Prefer actors over classes with locks
2. @Observable over ObservableObject - Simpler, better performance
3. Structured concurrency - async/await, no completion handlers
4. String Catalogs - ALL user-facing text must be localized
5. Profile in Release - Always profile with -O optimization
6. Value types - Prefer structs over classes