xu-xiang/everything-claude-code-zh/swift-actor-persistence

public actor LocalRepository<T: Codable & Identifiable> where T.ID == String {
    private var cache: [String: T] = [:]
    private let fileURL: URL
 
    public init(directory: URL = .documentsDirectory, filename: String = "data.json") {
        self.fileURL = directory.appendingPathComponent(filename)
        // 在 init 期间同步加载（此时 actor 隔离尚未生效）
        self.cache = Self.loadSynchronously(from: fileURL)
    }
 
    // MARK: - 公共 API
 
    public func save(_ item: T) throws {
        cache[item.id] = item
        try persistToFile()
    }
 
    public func delete(_ id: String) throws {
        cache[id] = nil
        try persistToFile()
    }
 
    public func find(by id: String) -> T? {
        cache[id]
    }
 
    public func loadAll() -> [T] {
        Array(cache.values)
    }
 
    // MARK: - 私有方法
 
    private func persistToFile() throws {
        let data = try JSONEncoder().encode(Array(cache.values))
        try data.write(to: fileURL, options: .atomic)
    }
 
    private static func loadSynchronously(from url: URL) -> [String: T] {
        guard let data = try? Data(contentsOf: url),
              let items = try? JSONDecoder().decode([T].self, from: data) else {
            return [:]
        }
        return Dictionary(uniqueKeysWithValues: items.map { ($0.id, $0) })
    }
}

let repository = LocalRepository<Question>()
 
// 读取 —— 从内存缓存中进行快速 O(1) 查找
let question = await repository.find(by: "q-001")
let allQuestions = await repository.loadAll()
 
// 写入 —— 原子化地更新缓存并持久化到文件
try await repository.save(newQuestion)
try await repository.delete("q-001")

@Observable
final class QuestionListViewModel {
    private(set) var questions: [Question] = []
    private let repository: LocalRepository<Question>
 
    init(repository: LocalRepository<Question> = LocalRepository()) {
        self.repository = repository
    }
 
    func load() async {
        questions = await repository.loadAll()
    }
 
    func add(_ question: Question) async throws {
        try await repository.save(question)
        questions = await repository.loadAll()
    }
}