Swift Language & Platform

You MUST use this skill for ANY Swift idiom review, ownership/noncopyable types, Transferable/drag-and-drop, debug deep links, or tvOS development.

Quick Reference

| Symptom / Task | Reference | |----------------|-----------| | Outdated Swift patterns (Date(), CGFloat, DateFormatter) | See skills/swift-modern.md | | Foundation modernization (FormatStyle, URL.documentsDirectory) | See skills/swift-modern.md | | Common Claude hallucinations in Swift code | See skills/swift-modern.md | | Noncopyable types (~Copyable) | See skills/ownership-conventions.md | | borrowing/consuming parameter ownership | See skills/ownership-conventions.md | | InlineArray, Span, value generics | See skills/ownership-conventions.md | | Reducing ARC overhead | See skills/ownership-conventions.md | | Drag and drop (.draggable, .dropDestination) | See skills/transferable-ref.md | | Copy/paste (.copyable, PasteButton) | See skills/transferable-ref.md | | ShareLink, content sharing | See skills/transferable-ref.md | | Custom UTType declarations | See skills/transferable-ref.md | | TransferRepresentation choices | See skills/transferable-ref.md | | Debug-only deep links for simulator testing | See skills/deep-link-debugging.md | | Navigate to specific screens for screenshots | See skills/deep-link-debugging.md | | tvOS Focus Engine, Siri Remote input | See skills/tvos.md | | tvOS storage constraints (no Documents dir) | See skills/tvos.md | | tvOS text input, AVPlayer tuning | See skills/tvos.md | | TVUIKit components | See skills/tvos.md |

Decision Tree

digraph swift {
    start [label="Swift task" shape=ellipse];
    what [label="What do you need?" shape=diamond];

    start -> what;
    what -> "skills/swift-modern.md" [label="modern idioms,\noutdated patterns,\nFoundation APIs"];
    what -> "skills/ownership-conventions.md" [label="~Copyable, borrowing,\nconsuming, InlineArray,\nSpan, ARC reduction"];
    what -> "skills/transferable-ref.md" [label="drag & drop, copy/paste,\nShareLink, UTTypes,\nTransferable conformance"];
    what -> "skills/deep-link-debugging.md" [label="debug deep links,\nsimulator navigation,\nscreenshot automation"];
    what -> "skills/tvos.md" [label="tvOS app,\nFocus Engine,\nSiri Remote, storage"];
}

Outdated Swift patterns / modern API replacements / Claude hallucinations? -> skills/swift-modern.md
~Copyable / borrowing / consuming / InlineArray / Span? -> skills/ownership-conventions.md
Drag and drop / copy/paste / ShareLink / Transferable / UTTypes? -> skills/transferable-ref.md
Debug deep links / simulator navigation / screenshot automation? -> skills/deep-link-debugging.md
tvOS development / Focus Engine / Siri Remote / storage / AVPlayer? -> skills/tvos.md
Swift concurrency (async/await, actors, Sendable) -> /skill axiom-concurrency
Swift performance (COW, ARC, generics optimization) -> See axiom-performance (skills/swift-performance.md)
Codable patterns (JSON, CodingKeys, enum serialization) -> See axiom-data (skills/codable.md)

Conflict Resolution

swift vs concurrency: When Swift 6 concurrency errors appear:

Use concurrency, NOT swift -- Concurrency errors are actor isolation / Sendable issues. skills/swift-modern.md covers concurrency posture (defaults), but detailed patterns live in axiom-concurrency.

swift vs performance: When optimizing Swift code:

Use swift for ownership if the question is borrowing/consuming/~Copyable/InlineArray/Span -> skills/ownership-conventions.md
Use performance if the question is COW, ARC profiling, generic specialization, or Instruments workflows -> axiom-performance

swift vs swiftui: When implementing drag and drop or copy/paste:

Use swift for Transferable conformance, representation choices, UTType declarations -> skills/transferable-ref.md
Use swiftui for view-level modifiers (.draggable, .dropDestination styling, animations)

swift vs integration: When sharing content:

ShareLink + Transferable -> use swift (skills/transferable-ref.md)
UIActivityViewController customization, share extensions -> use integration

swift vs axiom-build: When tvOS build fails:

Environment/Xcode issues -> use axiom-build first
tvOS platform-specific code issues (Focus Engine, storage, no WebView) -> use swift (skills/tvos.md)

Critical Patterns

Modern Swift Idioms (skills/swift-modern.md):

12+ outdated patterns Claude defaults to (Date(), CGFloat, DateFormatter, DispatchQueue.main.async)
Foundation modernization (FormatStyle, URL.documentsDirectory, .replacing())
SwiftUI convenience APIs Claude misses (ContentUnavailableView.search, LabeledContent)
Swift 6.3 concurrency posture defaults
9 common Claude hallucinations with corrections

Ownership & Noncopyable Types (skills/ownership-conventions.md):

borrowing/consuming parameter modifiers with 7 patterns
~Copyable types: FileHandle pattern, limitations table, common compiler errors
InlineArray: fixed-size stack-allocated arrays with value generics
Span family: safe contiguous memory access replacing UnsafeBufferPointer
Decision tree for when ownership modifiers help vs when to skip

Transferable & Sharing (skills/transferable-ref.md):

Decision tree: CodableRepresentation vs DataRepresentation vs FileRepresentation vs ProxyRepresentation
Drag and drop, copy/paste, ShareLink with complete SwiftUI API
Custom UTType declarations (Swift + Info.plist, both required)
7 common errors with fixes (representation ordering, missing Info.plist, hit testing)
UIKit bridging via NSItemProvider

Debug Deep Links (skills/deep-link-debugging.md):

Debug-only URL scheme for simulator navigation
NavigationPath integration for robust routing
State configuration links (error states, empty states)
Integration with /axiom:screenshot and simulator-tester agent
60-75% faster iteration with visual verification

tvOS Development (skills/tvos.md):

Dual focus system (UIKit Focus Engine + SwiftUI @FocusState)
Siri Remote input (two generations, three input layers)
Storage constraints (no Documents directory, iCloud required)
No WebView (JavaScriptCore only, no DOM)
AVPlayer tuning, Menu button state machine
TVUIKit components

Anti-Rationalization

| Thought | Reality | |---------|---------| | "Date() is fine, everyone uses it" | Date.now has been the modern pattern since Swift 5.6. skills/swift-modern.md lists 12+ patterns Claude gets wrong. | | "I don't need ownership modifiers" | For most code, correct. But ~Copyable types require them, and large value types in hot paths benefit measurably. | | "Transferable is just Codable for drag and drop" | Transferable has 4 representation types, ordering rules, and Info.plist requirements. Getting it wrong causes silent cross-app failures. | | "I'll just use the same code as iOS for tvOS" | tvOS has no Documents directory, no WebView, a dual focus system, and two generations of remote hardware. It compiles fine and fails at runtime. | | "Debug deep links are overkill" | Manual navigation costs 2-3 minutes per iteration. Deep links cut it to 45 seconds. Over a debugging session, that's hours saved. | | "CGFloat is what SwiftUI uses" | Swift 5.5+ has implicit Double-CGFloat bridging. Use Double everywhere except optionals, inout, and ObjC-bridged APIs. | | "I'll add the Info.plist entry later" | Custom UTTypes work in-app without Info.plist but silently fail cross-app. This is the #1 "works in dev, fails in prod" Transferable issue. | | "FormatStyle is too verbose" | val.formatted(.number.precision(.fractionLength(2))) is type-safe and localized. String(format:) is neither. |

Example Invocations

User: "Is this Swift code using modern patterns?" -> Read: skills/swift-modern.md

User: "How do I use borrowing and consuming?" -> Read: skills/ownership-conventions.md

User: "How do I make my model draggable?" -> Read: skills/transferable-ref.md

User: "How do I implement ShareLink with a custom preview?" -> Read: skills/transferable-ref.md

User: "I need debug deep links for simulator testing" -> Read: skills/deep-link-debugging.md

User: "I'm building a tvOS app and focus navigation doesn't work" -> Read: skills/tvos.md

User: "What is InlineArray and when should I use it?" -> Read: skills/ownership-conventions.md

User: "My drag and drop works in-app but not across apps" -> Read: skills/transferable-ref.md

User: "tvOS keeps losing my saved data" -> Read: skills/tvos.md

User: "How do I optimize large struct passing?" -> Read: skills/ownership-conventions.md

User: "I need to fix my async/await code" -> See /skill axiom-concurrency

User: "Check my code for Swift 6 concurrency issues" -> See /skill axiom-concurrency