【Swift/Combine】handleEventsメソッドの使い方と役割！イベント取得

func handleEvents(
    receiveSubscription: ((Subscription) -> Void)? = nil,
    receiveOutput: ((Self.Output) -> Void)? = nil,
    receiveCompletion: ((Subscribers.Completion<Self.Failure>) -> Void)? = nil,
    receiveCancel: (() -> Void)? = nil,
    receiveRequest: ((Subscribers.Demand) -> Void)? = nil
) -> Publishers.HandleEvents<Self>

let publisher = Deferred {
    Future<String, Never>() { promise in
        print("In Future")
        DispatchQueue.main.asyncAfter(deadline: .now() + 2) {
            promise(.success("成功したよ"))
        }
    }
}

let cancellable = publisher
    .handleEvents(
        receiveSubscription: { subs in
            print("Subscription: \(subs.combineIdentifier)")
        }, receiveOutput: { anInt in
            print("in output handler, received \(anInt)")
        }, receiveCompletion: { _ in
            print("in completion handler")
        }, receiveCancel: {
            print("received cancel")
        }, receiveRequest: { (demand) in
            print("received demand: \(demand.description)")
        }
    ).sink { _ in return }

In Future
Subscription: 0x600002108aa0
received demand: unlimited
in output handler, received 成功したよ
in completion handler

let cancellable = publisher
    .handleEvents(
        receiveOutput: { anInt in
            print("in output handler, received \(anInt)")
        }
    ).sink { _ in return }