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.