What problem does it solve? Swift's concurrency model changed significantly in Swift 6.2, and most guidance and training data still reflects outdated patterns, leading to data races, hangs, retain cycles, and misused actors. This Skill provides current, opinionated rules for writing idiomatic Swift through Swift 6.3/6.4. ## Core Features & Use Cases - Modern Concurrency Guidance: Covers the Swift 6.2 model where async no longer switches actors, plus @concurrent, nonisolated, actors, task groups, and Sendable diagnostics. - Value-Type Modeling & API Design: Rules for structs vs classes, copy-on-write, noncopyable types, some vs any, protocols, and generics. - Performance, ARC, and Testing: Concrete levers like InlineArray, Span, and final, plus Swift Testing patterns with @Test, #expect, and parameterized tests. - Use Case: When a data-race error appears after migrating to Swift 6, use this Skill to work down the fix hierarchy: stop sharing, make it a Sendable value type, isolate to an actor, then reach for Mutex. ## Quick Start Ask the assistant to review your Swift file for Swift 6 concurrency correctness and idiomatic value-type design.
