htc_3_28.swift

class ViewController: UIViewController {
    var cancellables: Set<AnyCancellable> = []
}
enum InputEvent {
    case newUserWasLoaded(User)
    var user: User {
        switch self {
        case .newUserWasLoaded(let user):
            return user
        }
    }
}
enum OutputEvent {
    case newsStateStepWasUpdated(NewsState.Step)
}
class NewsStore {
    @Published private(set) var state: NewsState
    private let input: AnyPublisher<InputEvent, Never>
    private let reducer: (NewsState, NewsEvent) -> NewsState
    init(
        initialState: NewsState,
        input: AnyPublisher<InputEvent, Never>,
        reducer: @escaping (NewsState, NewsEvent) -> NewsState
    ) {
        self.state = initialState
        self.reducer = reducer
        self.input = input
    }
    func accept(event: NewsEvent) {
        state = reducer(state, event)
    }
    func start() -> (UIViewController, AnyPublisher<OutputEvent, Never>) {
        let viewController = ViewController()
        input
            .map(\.user)
            .sink { self.state.user = $0 }
            .store(in: &viewController.cancellables)
        let output = $state
            .map(\.step)
            .map(OutputEvent.newsStateStepWasUpdated)
            .setFailureType(to: Never.self)
            .eraseToAnyPublisher()
        return (viewController, output)
    }
}