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Outdated Swift patterns (Date(), CGFloat, DateFormatter)	See skills/swift-modern.md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"];
}

1. Outdated Swift patterns / modern API replacements / Claude hallucinations? -> skills/swift-modern.md
2. ~Copyable / borrowing / consuming / InlineArray / Span? -> skills/ownership-conventions.md
3. Drag and drop / copy/paste / ShareLink / Transferable / UTTypes? -> skills/transferable-ref.md
4. Debug deep links / simulator navigation / screenshot automation? -> skills/deep-link-debugging.md
5. tvOS development / Focus Engine / Siri Remote / storage / AVPlayer? -> skills/tvos.md
6. Swift concurrency (async/await, actors, Sendable) -> /skill axiom-concurrency
7. Swift performance (COW, ARC, generics optimization) -> See axiom-performance (skills/swift-performance.md)
8. 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