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| Outdated Swift patterns (Date(), CGFloat, DateFormatter) | See skills/swift-modern.md |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}- Outdated Swift patterns / modern API replacements / Claude hallucinations?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.mdcovers 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