SwiftUI macOS

name: swiftui-macos description: Expert SwiftUI guidance for macOS apps — covers writing and reviewing code with runtime-level understanding of observation, concurrency, performance, and platform integration. Use when user asks to "build a SwiftUI view", "review my SwiftUI code", "fix observation issues", "bridge AppKit", "architect state management", "debug view updates", or works on any macOS SwiftUI project — building features, reviewing existing code, debugging view updates or performance, fixing concurrency issues, architecting state management, bridging AppKit, or making design decisions. Do NOT use for iOS/iPadOS-only SwiftUI, UIKit bridging, or basic Swift language questions. Focuses on non-obvious traps and deep patterns, not basics. license: MIT compatibility: Requires macOS 26+ targeting and Swift 6.2 with strict concurrency. Best suited for Claude Code and environments with filesystem access to load references on demand. metadata: author: kageroumado version: 1.0.0

Guide SwiftUI development for macOS apps. Whether writing new code or reviewing existing code, apply deep understanding of SwiftUI's runtime behavior — how the observation registrar dispatches, how the attribute graph diffs view trees, how actor isolation interacts with view lifecycles.

How to Use

Writing code: Load relevant references before implementation. The patterns here prevent bugs that are expensive to find later — observation cascades, identity thrashing, concurrency overhead. When making architecture decisions (state ownership, view decomposition, AppKit bridging), consult the relevant reference for tradeoffs.

Reviewing code: Check each reference area systematically. Focus on genuine problems — observation inefficiencies, deprecated API, accessibility gaps, concurrency anti-patterns. Don't flag obvious issues or invent problems.

Partial scope: Load only what the task needs. Not every change requires all eight references.

References

Principles

• Target macOS 26+, Swift 6.2 with strict concurrency and @MainActor default isolation.
• Check whether the project enables NonisolatedNonsendingByDefault (SE-0461) — this changes where nonisolated async functions execute. See references/concurrency.md.
• Prefer SwiftUI-native solutions. Use AppKit (NSViewRepresentable, NSHostingView, NSWindow) only when SwiftUI has no equivalent.
• Understand the mechanism. When suggesting a pattern, know why it works — what the observation registrar does, what the attribute graph diffing costs, what _modify vs set means for notification. Rules without understanding produce cargo-culted code.
• Do not introduce third-party frameworks without asking. Apple's open-source Swift packages (swift-collections, swift-algorithms, swift-async-algorithms) are exceptions — prefer them over reimplementing non-trivial data structures or algorithms. See references/api.md.

Examples

User: "Review observation patterns in these sidebar views" → Load references/observation.md. Check each file for: state capture in ForEach, non-Equatable types on observed properties, missing @ObservationIgnored on caches, _modify vs set notification waste.

User: "I need to embed an NSCollectionView in SwiftUI" → Load references/platform.md. Apply NSViewRepresentable lifecycle, Equatable conformance for update gating, Coordinator for delegates.

User: "This view is re-rendering too much, help me debug it" → Load references/performance.md and references/observation.md. Check view identity (structural vs explicit), observation scope (are unrelated properties tracked in the same body?), @State vs @Observable for gesture-driven values.

Review Output

Organize findings by file. For each issue:

1. File and relevant line(s).
2. The pattern being violated and why it matters at the runtime level.
3. Brief before/after code fix.

Skip clean files. End with a prioritized summary of the most impactful changes.