swift - 为什么 subscribe(subject) 返回 AnyCancellable 但 subscribe(subscriber) Void？

Question

我正在使用 Swift Joint，但不明白两者之间的区别

func subscribe<S>(_ subscriber: S) where S : Subscriber, Self.Failure == S.Failure, Self.Output == S.Input

和

func subscribe<S>(_ subject: S) -> AnyCancellable where S : Subject, Self.Failure == S.Failure, Self.Output == S.Output

为什么一个返回 AnyCancellable 而另一个返回 Void？

我有一个自定义订阅者，所以我使用它完全安全

myPublisher.subscribe(myCustomSubscriber)

无需处理AnyCancellable？

Answer 1

更新:

正如我下面的解释，您的自定义 Subscriber (我在下面的代码中将其命名为 MySubscriber )应该实现 Cancellable协议(protocol)。现在，您可以通过将订阅添加到 Set<AnyCancellable> 来管理订阅。 。当订阅者被取消时，订阅也会被取消。

<小时/>

我也有同样的担忧。我有一个自定义订阅者 Subscribers.MySubscriber并想添加功能Publisher.mySubscriber()就像Combine 对 Subscribers.Sink 所做的那样和Publisher.sink() 。但我不知道怎么办Publisher.sink()可以返回 AnyCancellable 。几分钟后，我猜测如何解决Publisher.sink()已实现:

extension Publisher {
    public func mySink(receiveCompletion: @escaping ((Subscribers.Completion<Self.Failure>) -> Void), receiveValue: @escaping ((Self.Output) -> Void)) -> AnyCancellable {
        let sink = Subscribers.Sink<Self.Output, Self.Failure>(receiveCompletion: receiveCompletion, receiveValue: receiveValue)
        subscribe(sink)
        return AnyCancellable(sink)
    }
}

所以定制订阅者应该符合Cancellable ，并保留订阅引用，以便在订阅者的 cancel() 调用时取消订阅，如下所示:

final class MySubscriber<Input, Failure: Error>: Subscriber, Cancellable {

    var subscription: Subscription?
    
    // ...
    
    init() {}

    func receive(subscription: Subscription) {
        // ...
        self.subscription = subscription
    }

    func receive(_ input: Input) -> Subscribers.Demand {
        // ...
        return .unlimited
    }

    func receive(completion: Subscribers.Completion<Failure>) {
        // ...
    }

    func cancel() {
        subscription?.cancel()
        subscription = nil
    }
}

所以我的函数Publisher.mySubscriber()函数将是:

extension Publisher {
    public func mySubscriber() -> AnyCancellable {
        let mySubscriber = MySubscriber<Output, Failure>()
        subscribe(mySubscriber)
        return AnyCancellable(mySubscriber)
    }
}