modern-swift

# Modern Swift (6.2+)

Swift 6.2 introduces strict compile-time concurrency checking with async/await, actors, and Sendable constraints that prevent data races at compile time instead of runtime. This is the foundation of safe concurrent Swift.

## Overview

Modern Swift replaces older concurrency patterns (completion handlers, DispatchQueue, locks) with compiler-enforced safety. The core principle: if it compiles with strict concurrency enabled, it cannot have data races.

## Quick Reference

| Need | Use | NOT |
|------|-----|-----|
| Async operation | `async/await` | Completion handlers |
| Main thread work | `@MainActor` | `DispatchQueue.main` |
| Shared mutable state | `actor` | Locks, serial queues |
| Parallel tasks | `TaskGroup` | `DispatchGroup` |
| Thread safety | `Sendable` | `@unchecked` everywhere |

## Core Workflow

When writing async Swift code:
1. Mark async functions with `async`, call with `await`
2. Apply `@MainActor` to view models and UI-updating code
3. Use `actor` instead of locks for shared mutable state
4. Check `Task.isCancelled` or call `Task.checkCancellation()` in loops
5. Enable strict concurrency in Package.swift for compile-time safety

## Reference Loading Guide

**ALWAYS load reference files if there is even a small chance the content may be required.** It's better to have the context than to miss a pattern or make a mistake.

| Reference | Load When |
|-----------|-----------|
| **[Concurrency Essentials](references/concurrency-essentials.md)** | Writing async code, converting completion handlers, using `await` |
| **[Swift 6 Concurrency](references/swift6-concurrency.md)** | Using `@concurrent`, `nonisolated(unsafe)`, or actor patterns |
| **[Task Groups](references/task-groups.md)** | Running multiple async operations in parallel |
| **[Task Cancellation](references/task-cancellation.md)** | Implementing long-running or cancellable operations |
| **[Strict Concurrency](references/strict-concurrency.md)** | Enabling Swift 6 stric