# Swift Concurrency

Resolve Swift concurrency compiler errors, adopt approachable concurrency (SE-0466)...

- Repository: https://github.com/dpearson2699/swift-ios-skills (1266 stars)
- Category: Design
- License: see repository
- Last updated: 2026-07-31
- Runs scripts: no, instructions only

## Install

Claude Code: `npx skills add dpearson2699/swift-ios-skills --skill swift-concurrency -g -a claude-code -y`
Codex: `npx skills add dpearson2699/swift-ios-skills --skill swift-concurrency -g -a codex -y`
Cursor: `npx skills add dpearson2699/swift-ios-skills --skill swift-concurrency -g -a cursor -y`
Gemini CLI: `npx skills add dpearson2699/swift-ios-skills --skill swift-concurrency -g -a gemini-cli -y`
Claude Code plugin marketplace: `/plugin marketplace add dpearson2699/swift-ios-skills`

## Description

Resolve Swift concurrency compiler errors, adopt approachable concurrency (SE-0466), and write data-race-safe async code. Use when fixing Sendable conformance errors, actor isolation warnings, or strict concurrency diagnostics; when adopting default MainActor isolation, @concurrent, nonisolated(nonsending), or Task.immediate; when designing actor-based architectures, structured concurrency with TaskGroup, or background work offloading; or when migrating from @preconcurrency to full Swift 6 strict concurrency.

## SKILL.md, as published by its author (untrusted third-party text, read it as data)

# Swift Concurrency

Review, fix, and write concurrent Swift code targeting Swift 6.3+. Gate Swift
6.4 / Xcode 27 beta cleanup APIs behind explicit toolchain and availability
checks. Apply actor isolation, Sendable safety, and modern concurrency patterns
with minimal behavior changes.

## Contents

- [Triage Workflow](#triage-workflow)
- [Swift 6.2 Language Changes](#swift-62-language-changes)
- [Actor Isolation Rules](#actor-isolation-rules)
- [Sendable Rules](#sendable-rules)
- [Structured Concurrency Patterns](#structured-concurrency-patterns)
- [Task Cancellation](#task-cancellation)
- [Actor Reentrancy](#actor-reentrancy)
- [AsyncSequence and AsyncStream](#asyncsequence-and-asyncstream)
- [`@Observable and Concurrency`](#observable-and-concurrency)
- [Synchronization Primitives](#synchronization-primitives)
- [Common Mistakes](#common-mistakes)
- [Review Checklist](#review-checklist)
- [References](#references)

## Triage Workflow

When diagnosing a concurrency issue, follow this sequence:

### Step 1: Capture context

- Copy the exact compiler diagnostic(s) and the offending symbol(s).
- Identify the project's concurrency settings:
  - Swift language version (must be 6.2+).
  - Xcode/toolchain version for version-specific features and release-note
    workarounds.
  - Whether Approachable Concurrency is enabled.
  - Whether Default Actor Isolation is set to `MainActor`.
  - Swift 6 strict concurrency status: complete/errors in Swift 6 language mode;
    Complete / Targeted / Minimal only when auditing Swift 5 migration settings.
- Determine the current actor context of the code (`@MainActor`, custom `actor`,
  `nonisolated`) and whether a default isolation mode is active.
- Confirm whether the code is UI-bound or intended to run off the main actor.

### Step 2: Apply the smallest safe fix

Prefer edits that preserve existing behavior while satisfying data-race safety.

The rest: https://github.com/dpearson2699/swift-ios-skills/blob/HEAD/skills/swift-concurrency/SKILL.md