coding-best-practices

Review each class for single responsibility, check that abstractions use protocols instead of concrete dependencies, and verify subtypes honor their base contracts. This Skill walks through each SOLID principle with good and bad Swift examples and provides prioritized fixes.

Mark UI code with @MainActor, use actors for mutable shared state, and ensure types crossing concurrency boundaries conform to Sendable. Replace completion handlers with async/await and prefer structured concurrency with task groups over unstructured tasks.

Use SwiftData for new projects since it offers modern @Model macros, @Query integration with SwiftUI, and simpler migration via VersionedSchema. Core Data remains appropriate for legacy migrations, complex fetched results controllers, or features SwiftData does not yet support.

Yes, the review guidance covers both SwiftUI patterns like @StateObject, @Query, and environment injection, and AppKit patterns like NSViewController separation. It targets macOS 26 development with Swift 6 strict concurrency checking.

Retain cycles occur when closures strongly capture self while self holds the closure, common in observers and callbacks. Fix them with [weak self] capture lists and guard let self, or use unowned only when the referenced object is guaranteed to outlive the closure.