# Swift Concurrency Expert

> Swift concurrency review/fix: compiler errors, Sendable, isolation, remediation.

- Skill: `steipete-agent-scripts/swift-concurrency-expert` (Agent Skill, multi-file: 3 files)
- Install (CLI): `npx skillmds add steipete-agent-scripts/swift-concurrency-expert`
- Raw SKILL.md: https://api.skillmd.com/api/skills/steipete-agent-scripts/swift-concurrency-expert/raw
- Safety review: pending
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: steipete (https://skillmd.com/u/steipete-agent-scripts)
- Updated: 2026-09-09
- Page: https://skillmd.com/skills/steipete-agent-scripts/swift-concurrency-expert

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# Swift Concurrency Expert

_Attribution: copied from @Dimillian’s `Dimillian/Skills` (2025-12-31)._

## Overview

Review and fix Swift Concurrency issues in Swift 6.2+ codebases by applying actor isolation, Sendable safety, and modern concurrency patterns with minimal behavior changes.

## Workflow

### 1. Triage the issue

- Capture the exact compiler diagnostics and the offending symbol(s).
- Identify the current actor context (`@MainActor`, `actor`, `nonisolated`) and whether a default actor isolation mode is enabled.
- Confirm whether the code is UI-bound or intended to run off the main actor.

### 2. Apply the smallest safe fix

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

Common fixes:
- **UI-bound types**: annotate the type or relevant members with `@MainActor`.
- **Protocol conformance on main actor types**: make the conformance isolated (e.g., `extension Foo: @MainActor SomeProtocol`).
- **Global/static state**: protect with `@MainActor` or move into an actor.
- **Background work**: move expensive work into a `@concurrent` async function on a `nonisolated` type or use an `actor` to guard mutable state.
- **Sendable errors**: prefer immutable/value types; add `Sendable` conformance only when correct; avoid `@unchecked Sendable` unless you can prove thread safety.


## Reference material

- See `references/swift-6-2-concurrency.md` for Swift 6.2 changes, patterns, and examples.
- See `references/swiftui-concurrency-tour-wwdc.md` for SwiftUI-specific concurrency guidance.