class Demo5 {
    var cancellables = Set<AnyCancellable>()
    
    func example(of: String) {
        let pub1 = PassthroughSubject<Int, Never>()
        let pub2 = PassthroughSubject<Int, Never>()
        let pub3 = PassthroughSubject<Int, Never>()

        let publishers = PassthroughSubject<PassthroughSubject<Int, Never>, Never>()
        
        
        publishers
            .switchToLatest()
            .sink(receiveCompletion: { _ in print("Completed!") },
                  receiveValue: { print($0) })
            .store(in: &cancellables)
        
        
        publishers.send(pub1)
        pub1.send(1)
        pub1.send(2)
        
        
        publishers.send(pub2)
        pub1.send(3)
        pub2.send(4)
        pub2.send(5)
        
        
        publishers.send(pub3)
        pub2.send(6)
        pub3.send(7)
        pub3.send(8)
        pub3.send(9)

        pub3.send(completion: .finished)
        publishers.send(completion: .finished)

    }
}

let d = Demo5()
d.example(of: "good")

let pub = PassthroughSubject<Int, Never>()

let cancellable = pub
    .setFailureType(to: URLError.self)
    .map() { index -> URLSession.DataTaskPublisher in
        let url = URL(string: "https://example.org/get?index=\(index)")!
        return URLSession.shared.dataTaskPublisher(for: url)
    }
    .switchToLatest()
    .sink(receiveCompletion: { print("Complete: \($0)") },
          receiveValue: { (data, response) in
            guard let url = response.url else {
                print("Bad response."); return
            }
            print("URL: \(url)")
    })


for i in 1...5 {
    DispatchQueue.main.asyncAfter(deadline: .now() + TimeInterval(i/10)) {
        pub.send(i)
    }
}

struct Feedback<State, Event> {
    let run: (AnyPublisher<State, Never>) -> AnyPublisher<Event, Never>
}


extension Feedback {
    init<Effect: Publisher>
    (effects: @escaping (State) -> (Effect))
    where Effect.Output == Event, Effect.Failure == Never
    
    {
        self.run = { statePub -> AnyPublisher<Event, Never> in
            statePub
                .map { effects($0) } // Effect  Publisher<Event, Never>
                .switchToLatest() // Event
                .eraseToAnyPublisher() // AnyPublisher<Event, Never>
        }
    }
}