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Swift language patterns and best practices including concurrency, performance, and modern idioms.
Passed 22 of 23 test cases with the skill, and 19 of 23 without it.
3 fixed19 passed either way1 still failing0 broke
Tokens, turns and time describe resource use, not a dollar price.
One of 3 test cases the skill fixed. Same model, same prompt, with and without the skill.
I have an async helper function `fetchLocalData()` that reads from local storage. In Swift 6.0 it ran on a background thread from the global cooperative pool, but after upgrading to Swift 6.2, callers on the main thread experience frame drops because `fetchLocalData()` runs directly on the main thread. How do I force this async function off the caller's executor without turning it into an actor method?
| Checked | Without skill | With skill |
|---|---|---|
| Recommends marking the function with the @concurrent attribute | Missed | Passed |
The instructions your model reads when the skill loads.
Swift language-level guidance that applies across all Apple platforms.
Use this skill when the user:
Swift concurrency architecture and patterns.
nonisolated(nonsending), Apple's adoption doctrine)Swift 6.2 concurrency updates reference — the what-changed view (async-stays-on-caller, default MainActor inference, isolated conformances, @concurrent) with migration steps from 6.0/6.1 and top mistakes. Overlaps concurrency-patterns/swift62-concurrency.md by design: use this file when the question is "what changed in 6.2?", use concurrency-patterns when building or reviewing async code.
Complexity and size limits for Swift code — SwiftLint threshold rules (cyclomatic complexity, function/type/file length, parameter count) with a violations-baseline adoption path so existing code never blocks. Part of the deterministic gauntlet with testing/fitness-functions and testing/coverage-ratchet.
InlineArray, Span, and the Swift performance cost model.
swift-performance.md: the cost model — allocation, ARC/retain-release, exclusivity checks, dispatch, generics vs existentials, closures, ~Copyable ownershiptest cases passed, vs 19 / 23 without
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