Throw运算

Never运算

Empty运算

extension Observable {
    public static func empty()->Observable<E> {
        return Empty<E>()
    }

    public static func never()->Observable<E> {
        return Never()
    }
}

class Empty<Element>: Producer<Element> {
    override func subscribe<O: ObserverType where O.E == Element>(observer: O)->Disposable {
        observer.on(.Completed)
        return NoDisposable.instance
    }
}

class Never<Element>: Producer<Element> {
    override func subscribe<O: ObserverType where O.E == Element>(observer: O)->Disposable {
        return NoDisposable.instance
    }
}