Extension to create an AnyPublisher to easily 'lift' async code into Combine

AnyPublisher+Extension.swift

extension AnyPublisher where Failure: Error {
    struct Subscriber {
        fileprivate let send: (Output) -> Void
        fileprivate let complete: (Subscribers.Completion<Failure>) -> Void

        func send(_ value: Output) { self.send(value) }
        func send(completion: Subscribers.Completion<Failure>) { self.complete(completion) }
    }

    init(_ closure: (Subscriber) -> AnyCancellable) {
        let subject = PassthroughSubject<Output, Failure>()

        let subscriber = Subscriber(
            send: subject.send,
            complete: subject.send(completion:)
        )
        let cancel = closure(subscriber)

        self = subject
            .handleEvents(receiveCancel: cancel.cancel)
            .eraseToAnyPublisher()
    }
}