Swift Concurrency Patterns
Expert guidance on Swift Concurrency best practices covering async/await, actors, tasks, Sendable, threading, memory management, testing, and migration strategies.
Rules
Core Swift Concurrency rules extracted as discrete, high-impact patterns. See rules index for the full list organized by:
- Async/Await Patterns - Never add dummy suspension points to silence warnings
- Actor Isolation - Use actors for data-race safety with compiler verification
- Task Lifecycle - Understand task cancellation and structured concurrency
- Sendable Conformance - Require Sendable for crossing concurrency boundaries
- Testing - Patterns for testing async concurrent code without flaky tests
References
See references/swift-concurrency.md for comprehensive guidance organized by:
- Async/Await Fundamentals - Core patterns, error handling, parallel execution
- Tasks & Structured Concurrency - Task lifecycle, cancellation, task groups
- Actors & Isolation - Actor isolation, suspension points, state safety
- Sendable & Data Safety - Sendable conformance, data races, safe captures
- Threading & Execution - Execution contexts, isolation domains
- Memory Management - Retain cycles, weak references, task lifecycle
- Testing Concurrency - Async test patterns, Swift Testing integration
- Migration & Interop - Strict concurrency migration, legacy interop
Examples
Positive Trigger
User: "Refactor callback-based network code to async/await with actor isolation."
Expected behavior: Use swift-concurrency guidance, follow its workflow, and return actionable output.
Non-Trigger
User: "Refactor CSS grid layout for mobile breakpoints."
Expected behavior: Do not prioritize swift-concurrency; choose a more relevant skill or proceed without it.
Troubleshooting
Skill Does Not Trigger
- Error: The skill is not selected when expected.
- Cause: Request wording does not clearly match the description trigger conditions.
- Solution: Rephrase with explicit domain/task keywords from the description and retry.
Guidance Conflicts With Another Skill
- Error: Instructions from multiple skills conflict in one task.
- Cause: Overlapping scope across loaded skills.
- Solution: State which skill is authoritative for the current step and apply that workflow first.
Output Is Too Generic
- Error: Result lacks concrete, actionable detail.
- Cause: Task input omitted context, constraints, or target format.
- Solution: Add specific constraints (environment, scope, format, success criteria) and rerun.
Workflow
- Identify whether the request clearly matches
swift-concurrency scope and triggers.
- Apply the skill rules and referenced guidance to produce a concrete result.
- Validate output quality against constraints; if gaps remain, refine once with explicit assumptions.
1---2name: swift-concurrency3description: Swift Concurrency patterns — async/await, actors, tasks, Sendable conformance. Use when writing async/await code, implementing actors, working with structured concurrency, or ensuring data race safety.4---56# Swift Concurrency Patterns78Expert guidance on Swift Concurrency best practices covering async/await, actors, tasks, Sendable, threading, memory management, testing, and migration strategies.910## Rules1112Core Swift Concurrency rules extracted as discrete, high-impact patterns. See [rules index](rules/_sections.md) for the full list organized by:1314- **Async/Await Patterns** - Never add dummy suspension points to silence warnings15- **Actor Isolation** - Use actors for data-race safety with compiler verification16- **Task Lifecycle** - Understand task cancellation and structured concurrency17- **Sendable Conformance** - Require Sendable for crossing concurrency boundaries18- **Testing** - Patterns for testing async concurrent code without flaky tests1920## References2122See [references/swift-concurrency.md](references/swift-concurrency.md) for comprehensive guidance organized by:2324- **Async/Await Fundamentals** - Core patterns, error handling, parallel execution25- **Tasks & Structured Concurrency** - Task lifecycle, cancellation, task groups26- **Actors & Isolation** - Actor isolation, suspension points, state safety27- **Sendable & Data Safety** - Sendable conformance, data races, safe captures28- **Threading & Execution** - Execution contexts, isolation domains29- **Memory Management** - Retain cycles, weak references, task lifecycle30- **Testing Concurrency** - Async test patterns, Swift Testing integration31- **Migration & Interop** - Strict concurrency migration, legacy interop3233## Examples3435### Positive Trigger3637User: "Refactor callback-based network code to async/await with actor isolation."3839Expected behavior: Use `swift-concurrency` guidance, follow its workflow, and return actionable output.4041### Non-Trigger4243User: "Refactor CSS grid layout for mobile breakpoints."4445Expected behavior: Do not prioritize `swift-concurrency`; choose a more relevant skill or proceed without it.4647## Troubleshooting4849### Skill Does Not Trigger5051- Error: The skill is not selected when expected.52- Cause: Request wording does not clearly match the description trigger conditions.53- Solution: Rephrase with explicit domain/task keywords from the description and retry.5455### Guidance Conflicts With Another Skill5657- Error: Instructions from multiple skills conflict in one task.58- Cause: Overlapping scope across loaded skills.59- Solution: State which skill is authoritative for the current step and apply that workflow first.6061### Output Is Too Generic6263- Error: Result lacks concrete, actionable detail.64- Cause: Task input omitted context, constraints, or target format.65- Solution: Add specific constraints (environment, scope, format, success criteria) and rerun.6667## Workflow68691. Identify whether the request clearly matches `swift-concurrency` scope and triggers.702. Apply the skill rules and referenced guidance to produce a concrete result.713. Validate output quality against constraints; if gaps remain, refine once with explicit assumptions.
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