struct User: Identifiable, Codable {
    let id: UUID
    var name: String
    var email: String

    var displayName: String {
        name.capitalized
    }
}

// Prefer structs for data
struct User: Identifiable, Codable, Hashable {
    let id: UUID
    var name: String
    var email: String
    var createdAt: Date = .now
}

// Enums with associated values
enum NetworkError: Error, LocalizedError {
    case invalidURL
    case noData
    case decodingError(Error)

    var errorDescription: String? {
        switch self {
        case .invalidURL: return "Invalid URL"
        case .noData: return "No data received"
        case .decodingError(let error): return "Decoding failed: \(error)"
        }
    }
}

protocol Repository {
    associatedtype Entity: Identifiable

    func findById(_ id: Entity.ID) async throws -> Entity?
    func save(_ entity: Entity) async throws -> Entity
    func delete(_ entity: Entity) async throws
}

extension Repository {
    func saveAll(_ entities: [Entity]) async throws -> [Entity] {
        try await withThrowingTaskGroup(of: Entity.self) { group in
            for entity in entities {
                group.addTask { try await self.save(entity) }
            }
            return try await group.reduce(into: []) { $0.append($1) }
        }
    }
}

func fetchUser(id: UUID) async throws -> User {
    let url = URL(string: "https://api.example.com/users/\(id)")!
    let (data, response) = try await URLSession.shared.data(from: url)

    guard let httpResponse = response as? HTTPURLResponse,
          httpResponse.statusCode == 200 else {
        throw NetworkError.invalidResponse
    }

    return try JSONDecoder().decode(User.self, from: data)
}

// Parallel execution
async let user = fetchUser(id: userId)
async let orders = fetchOrders(userId: userId)
let (userResult, ordersResult) = try await (user, orders)

actor UserCache {
    private var cache: [UUID: User] = [:]

    func get(_ id: UUID) -> User? { cache[id] }
    func set(_ user: User) { cache[user.id] = user }
}