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Guide Swift Concurrency by prisma-labs-dev

Name: Guide Swift Concurrency
Rating: 4.2 (5 reviews)
Author: prisma-labs-dev

Guide Swift Concurrency

Swift concurrency patterns — actors, structured concurrency, cancellation, async streams, GCD migration, strict-concurrency diagnostics, common bug patterns. Use when writing, reviewing, or debugging concurrent Swift code.

prisma-labs-dev f1ec1ec 13 files · 52.8 KB Updated Sep 9, 2026

File contents

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

Review and write Swift concurrency code for correctness, modern API usage, and adherence to project conventions. Report only genuine problems — do not nitpick or invent issues.

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

Scan for known-dangerous patterns using references/hotspots.md.
Check for Swift 6.2 concurrency behavior using references/new-features.md.
Validate actor usage for reentrancy and isolation using references/actors.md.
Ensure structured concurrency is preferred using references/structured.md.
Check unstructured task usage using references/unstructured.md.
Verify cancellation handling using references/cancellation.md.
Validate async stream and continuation usage using references/async-streams.md.
Check bridging code between sync and async using references/bridging.md.
Review legacy concurrency migrations using references/interop.md.
Cross-check against common failure modes using references/bug-patterns.md.
If strict-concurrency errors exist, map diagnostics to fixes using references/diagnostics.md.
If reviewing tests, check async test patterns using references/testing.md.

If doing partial work, load only the relevant reference files.

References

Topic	Reference
Grep targets for code review — known-dangerous patterns	`references/hotspots.md`
Swift 6.2: default isolation, `@concurrent`, `Task.immediate`, isolated deinit	`references/new-features.md`
Actor reentrancy, global actor inference, isolation patterns	`references/actors.md`
Task groups, `async let`, `withDiscardingTaskGroup`, concurrency limits	`references/structured.md`
`Task` vs `Task.detached`, when `Task {}` is a code smell	`references/unstructured.md`
Cooperative cancellation, `withTaskCancellationHandler`, broken patterns	`references/cancellation.md`
`AsyncStream.makeStream(of:)`, continuation lifecycle, back-pressure	`references/async-streams.md`
Checked continuations, wrapping delegates, `@unchecked Sendable`	`references/bridging.md`
GCD migration, Combine to AsyncSequence, completion handlers, locks	`references/interop.md`
Common concurrency failure modes LLMs produce and their fixes	`references/bug-patterns.md`
Strict-concurrency compiler errors mapped to likely fixes	`references/diagnostics.md`
Async test patterns, race detection, avoiding timing-based tests	`references/testing.md`

---name: guide-swift-concurrencydescription: Swift concurrency patterns — actors, structured concurrency, cancellation, async streams, GCD migration, strict-concurrency diagnostics, common bug patterns. Use when writing, reviewing, or debugging concurrent Swift code.license: MIT--- > **Guide Skill** — This is an expert workflow/pattern guide, not API reference documentation. > Originally from [twostraws/Swift-Concurrency-Agent-Skill](https://github.com/twostraws/Swift-Concurrency-Agent-Skill) by Paul Hudson. MIT License. # Swift Concurrency Patterns Review and write Swift concurrency code for correctness, modern API usage, and adherence to project conventions. Report only genuine problems — do not nitpick or invent issues. ## 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`. If doing partial work, load only the relevant reference files. ## References | Topic | Reference | |-------|-----------| | Grep targets for code review — known-dangerous patterns | `references/hotspots.md` | | Swift 6.2: default isolation, `@concurrent`, `Task.immediate`, isolated deinit | `references/new-features.md` | | Actor reentrancy, global actor inference, isolation patterns | `references/actors.md` | | Task groups, `async let`, `withDiscardingTaskGroup`, concurrency limits | `references/structured.md` | | `Task` vs `Task.detached`, when `Task {}` is a code smell | `references/unstructured.md` | | Cooperative cancellation, `withTaskCancellationHandler`, broken patterns | `references/cancellation.md` | | `AsyncStream.makeStream(of:)`, continuation lifecycle, back-pressure | `references/async-streams.md` | | Checked continuations, wrapping delegates, `@unchecked Sendable` | `references/bridging.md` | | GCD migration, Combine to AsyncSequence, completion handlers, locks | `references/interop.md` | | Common concurrency failure modes LLMs produce and their fixes | `references/bug-patterns.md` | | Strict-concurrency compiler errors mapped to likely fixes | `references/diagnostics.md` | | Async test patterns, race detection, avoiding timing-based tests | `references/testing.md` |

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