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

1. Identify whether the request clearly matches swift-concurrency scope and triggers.
2. Apply the skill rules and referenced guidance to produce a concrete result.
3. Validate output quality against constraints; if gaps remain, refine once with explicit assumptions.