Guide Skill — This is an expert workflow/pattern guide, not API reference documentation. Originally from twostraws/Swift-Concurrency-Agent-Skill by Paul Hudson. MIT License.

Swift Concurrency Patterns

Core Instructions

• Target Swift 6.2 or later with strict concurrency checking.
• Prefer structured concurrency (task groups) over unstructured (

  Task {}

  ).
• Prefer Swift concurrency over GCD for new code. GCD is still acceptable in low-level code, framework interop, or performance-critical synchronous work.
• Do not suggest

  @unchecked Sendable

  to fix compiler errors — prefer actors, value types, or

  sending

  parameters.

Review Process

1. Scan for known-dangerous patterns using

   references/hotspots.md

   .
2. Check for Swift 6.2 concurrency behavior using

   references/new-features.md

   .
3. Validate actor usage for reentrancy and isolation using

   references/actors.md

   .
4. Ensure structured concurrency is preferred using

   references/structured.md

   .
5. Check unstructured task usage using

   references/unstructured.md

   .
6. Verify cancellation handling using

   references/cancellation.md

   .
7. Validate async stream and continuation usage using

   references/async-streams.md

   .
8. Check bridging code between sync and async using

   references/bridging.md

   .
9. Review legacy concurrency migrations using

   references/interop.md

   .
10. Cross-check against common failure modes using

    references/bug-patterns.md

    .
11. If strict-concurrency errors exist, map diagnostics to fixes using

    references/diagnostics.md

    .
12. If reviewing tests, check async test patterns using

    references/testing.md

    .

References

references/hotspots.md

@concurrent

Task.immediate

references/new-features.md

references/actors.md

async let

withDiscardingTaskGroup

references/structured.md

Task

Task.detached

Task {}

references/unstructured.md

withTaskCancellationHandler

references/cancellation.md

AsyncStream.makeStream(of:)

references/async-streams.md

@unchecked Sendable

references/bridging.md

references/interop.md

references/bug-patterns.md

references/diagnostics.md

references/testing.md