Swift Concurrency 6 2

// Swift 6.1: ERROR@MainActorfinal class StickerModel {    let photoProcessor = PhotoProcessor()
    func extractSticker(_ item: PhotosPickerItem) async throws -> Sticker? {        guard let data = try await item.loadTransferable(type: Data.self) else { return nil }
        // Error: Sending 'self.photoProcessor' risks causing data races        return await photoProcessor.extractSticker(data: data, with: item.itemIdentifier)    }}

// Swift 6.2: OK — async stays on MainActor, no data race@MainActorfinal class StickerModel {    let photoProcessor = PhotoProcessor()
    func extractSticker(_ item: PhotosPickerItem) async throws -> Sticker? {        guard let data = try await item.loadTransferable(type: Data.self) else { return nil }        return await photoProcessor.extractSticker(data: data, with: item.itemIdentifier)    }}

protocol Exportable {    func export()}
// Swift 6.1: ERROR — crosses into main actor-isolated code// Swift 6.2: OK with isolated conformanceextension StickerModel: @MainActor Exportable {    func export() {        photoProcessor.exportAsPNG()    }}

// OK — ImageExporter is also @MainActor@MainActorstruct ImageExporter {    var items: [any Exportable]
    mutating func add(_ item: StickerModel) {        items.append(item)  // Safe: same actor isolation    }}
// ERROR — nonisolated context can't use MainActor conformancenonisolated struct ImageExporter {    var items: [any Exportable]
    mutating func add(_ item: StickerModel) {        items.append(item)  // Error: Main actor-isolated conformance cannot be used here    }}

// Swift 6.1: ERROR — non-Sendable type may have shared mutable statefinal class StickerLibrary {    static let shared: StickerLibrary = .init()  // Error}
// Fix: Annotate with @MainActor@MainActorfinal class StickerLibrary {    static let shared: StickerLibrary = .init()  // OK}

// With MainActor default inference enabled:final class StickerLibrary {    static let shared: StickerLibrary = .init()  // Implicitly @MainActor}
final class StickerModel {    let photoProcessor: PhotoProcessor    var selection: [PhotosPickerItem]  // Implicitly @MainActor}
extension StickerModel: Exportable {  // Implicitly @MainActor conformance    func export() {        photoProcessor.exportAsPNG()    }}

nonisolated final class PhotoProcessor {    private var cachedStickers: [String: Sticker] = [:]
    func extractSticker(data: Data, with id: String) async -> Sticker {        if let sticker = cachedStickers[id] {            return sticker        }
        let sticker = await Self.extractSubject(from: data)        cachedStickers[id] = sticker        return sticker    }
    // Offload expensive work to concurrent thread pool    @concurrent    static func extractSubject(from data: Data) async -> Sticker { /* ... */ }}
// Callers must awaitlet processor = PhotoProcessor()processedPhotos[item.id] = await processor.extractSticker(data: data, with: item.id)