| name | swift-concurrency-expert |
| description | Swift Concurrency review and remediation for Swift 6.2+. Use when asked to review Swift Concurrency usage, improve concurrency compliance, or fix Swift concurrency compiler errors in a feature or file. |
Swift Concurrency Expert
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).
- Check project concurrency settings: Swift language version (6.2+), strict concurrency level, and whether approachable concurrency (default actor isolation / main-actor-by-default) is enabled.
- 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/approachable-concurrency.md when the project is opted into approachable concurrency mode.
- See
references/swiftui-concurrency-tour-wwdc.md for SwiftUI-specific concurrency guidance.
