gh-Dimillian-Skills/swift-concurrency-expert/references/swiftui-concurrency-tour-wwdc.md

SwiftUI Concurrency Tour (Summary)

Context: SwiftUI-focused concurrency overview covering actor isolation, Sendable closures, and how SwiftUI runs work off the main thread.

Main-actor default in SwiftUI

• View is @MainActor isolated by default; members and body inherit isolation.
• Swift 6.2 can infer @MainActor for all types in a module (new language mode).
• This default simplifies UI code and aligns with UIKit/AppKit @MainActor APIs.

Where SwiftUI runs code off the main thread

• SwiftUI may evaluate some view logic on background threads for performance.
• Examples: Shape path generation, Layout methods, visualEffect closures, and onGeometryChange closures.
• These APIs often require Sendable closures to reflect their runtime semantics.

Sendable closures and data-race safety

• Accessing @MainActor state from a Sendable closure is unsafe and flagged by the compiler.
• Prefer capturing value copies in the closure capture list (e.g., copy a Bool).
• Avoid sending self into a sendable closure just to read a single property.

Structuring async work with SwiftUI

• SwiftUI action callbacks are synchronous so UI updates (like loading states) can be immediate.
• Use Task to bridge into async contexts; keep async bodies minimal.
• Use state as the boundary: async work updates model/state; UI reacts synchronously.

Performance-driven concurrency

• Offload expensive work from the main actor to avoid hitches.
• Keep time-sensitive UI logic (animations, gesture responses) synchronous.
• Separate UI code from long-running async work to improve responsiveness and testability.