Swift 5.10\u20136.3 Knowledge Patch Skill

Swift 5.10\u20136.3 Knowledge Patch

Claude's baseline knowledge covers Swift through 5.9. This skill provides features from 5.10 (March 2024) through 6.3 (March 2026).

Quick Reference

Concurrency

| Feature | Summary | |---------|---------| | -default-isolation MainActor | All code MainActor-isolated by default (per module) | | @concurrent | Opt function into concurrent thread pool | | Nonisolated async | Runs on caller's actor by default (SE-0461) | | Task.immediate | Starts synchronously on caller's executor | | isolated deinit | Runs deinit on actor's executor | | weak let | Immutable weak ref, enables Sendable | | @MainActor Equatable | Actor-isolated protocol conformances | | Task(name:) | Named tasks for debugging |

// Enable approachable concurrency features per-target:
.enableUpcomingFeature("NonisolatedNonsendingByDefault")
.enableUpcomingFeature("InferIsolatedConformances")

See references/concurrency.md for full details and examples.

Language Features

| Feature | Example | |---------|---------| | InlineArray | var buf: InlineArray<40, Sprite> or [40 of Sprite] | | Method key paths | strings.map(\.uppercased()) | | Default interpolation | "\(age, default: "Unknown")" | | enumerated() | Now conforms to Collection | | Module selectors | ModuleA::getValue() | | @c attribute | Expose Swift functions to C |

See references/language-features.md for syntax, limitations, and examples.

Swift Testing

| Feature | API | |---------|-----| | Exit tests | #expect(processExitsWith: .failure) { ... } | | Attachments | Attachment.record("debug info") | | Warnings | Issue.record("msg", severity: .warning) | | Cancel test | try Test.cancel() |

See references/swift-testing.md for details.

New APIs

| API | Purpose | |-----|---------| | Observations { } | Async sequence from @Observable types | | Subprocess | Process execution (import Subprocess) | | Typed NotificationCenter | Type-safe notifications (no string names) |

See references/new-apis.md for details.

Reference Files

| File | Contents | |------|----------| | concurrency.md | MainActor default, @concurrent, Task.immediate, isolated deinit, weak let | | language-features.md | InlineArray, key paths, interpolation, module selectors, @c interop | | swift-testing.md | Exit tests, attachments, warnings, test cancellation | | new-apis.md | Observations, Subprocess, typed NotificationCenter |

Critical Examples

Approachable Concurrency (6.2)

// With -default-isolation MainActor, no annotations needed:
struct ImageCache {
    static var cache: [URL: Image] = [:]

    static func load(from url: URL) async throws -> Image {
        if let img = cache[url] { return img }
        let img = try await fetchImage(at: url) // stays on MainActor
        cache[url] = img
        return img
    }

    @concurrent // explicitly run off MainActor
    static func fetchImage(at url: URL) async throws -> Image {
        let (data, _) = try await URLSession.shared.data(from: url)
        return decode(data)
    }
}

InlineArray (6.2)

var bricks: InlineArray<40, Sprite> = .init(repeating: defaultSprite)
// Shorthand:
var bricks2: [40 of Sprite] = .init(repeating: defaultSprite)

bricks[0] = specialSprite
for i in bricks.indices { print(bricks[i]) } // use indices, not for-in

@c Attribute for C Interop (6.3)

@c func mySwiftFunction() { /* ... */ }
// Generated header: void mySwiftFunction(void);

@c(MyLib_doWork) func doWork() { /* ... */ }
// Generated header: void MyLib_doWork(void);

@c @implementation func existingCFunction() { /* ... */ }
// Validates against pre-existing C header declaration

Module Selectors (6.3)

import ModuleA
import ModuleB
let x = ModuleA::getValue()
let y = ModuleB::getValue()

// Access Swift concurrency types without ambiguity:
let task = Swift::Task { await doWork() }

Observations Async Sequence (6.2)

@Observable class Store { var items: [String] = []; var loading = false }
let store = Store()

let stream = Observations {
    (items: store.items, loading: store.loading) // tracks both properties
}
for await snapshot in stream {
    render(snapshot.items, snapshot.loading)
}

Swift Testing: Exit Tests (6.2)

@Test func preconditionFires() async {
    await #expect(processExitsWith: .failure) {
        precondition(false)
    }
}

Agent Skills: Swift 5.10\u20136.3 Knowledge Patch

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