zip3运算

class Zip3<E1, E2, E3, R> : Producer<R> {
typealias ResultSelector = (E1, E2, E3) throws->R

    let source1: Observable<E1>
    let source2: Observable<E2>
    let source3: Observable<E3>

    let _resultSelector: ResultSelector

    init(source1: Observable<E1>, source2: Observable<E2>, source3: Observable<E3>, resultSelector: ResultSelector) {
        self.source1 = source1
        self.source2 = source2
        self.source3 = source3

        _resultSelector = resultSelector
    }

    override func run<O: ObservableType where O.E == R>(observer: O)->Disposable {
        let sink = ZipSink3_(parent: self, observer: observer)
        sink.disposable = sink.run()
        return sink
    }
}

class ZipSink3_<E1, E2, E3, O: ObserverType> : ZipSink<O> {
    typealias R = O.E
    typealias Parent = Zip3<E1, E2, E3, R>

    let _parent : Parent

    var _values1: Queue<E1> = Queue(capacity: 2)
    var _values2: Queue<E2> = Queue(capacity: 2)
    var _values3: Queue<E3> = Queue(capacity: 2)

    init(parent: Parent, observer: O) {
        _parent = Parent
        super.init(arity: 3, observer: observer)
    }

    override func haselements(index: Int)->Bool {
        switch (index) {
        case 0: return _values1.count > 0
        case 1: return _values2.count > 0
        case 2: return _values3.count > 0

        default:
            rxFatalError("Unhandled case (Function)")
        }

        return false
    }

    func run()->Disposable {
        let subscription1 =         SingleAssignmentDisposable()
        let subscription2 = SingleAssignmentDisposable()
        let subscription3 = SingleAssignmentDisposable()

        let observer1 = ZipObserver(lock: _lock, parent: self, index: 0, setNextValue: { self._values1.enqueue($0) }, this: subscription1)
        let observer2 = ZipObserver(lock: _lock, parent: self, index: 1, setNextValue: { self._values2.enqueue($0) }, this: subscription2)
        let observer3 = ZipObserver(lock: _lock, parent: self, index: 2, setNextValue: { self._values3.enqueue($0) }, this: subscription3)

        subscription1.disposable = _parent.source1.subscribe(observer1)
        subscription2.disposable = _parent.source2.subscribe(observer2)
        subscription3.disposable = _parent.source3.subscribe(observer3)

        return CompositeDisposable(disposables: [
           subscription1,
           subscription2,
           subscription3
        ])
    }

    override func getResult() throws -> R {
        return try _parent._resultSelector(_values1.dequeue()!, _values2.dequeue()!, _values3.dequeue()!)
    }
}

extension Observable {
    public static func zip<01: observableType, 02: ObservableType, 03: ObservableType>(source1: 01, _ source2: 02, _ source3: 03, resultSelector: (01.E, 02.E, 03.E)throws -> E) -> Observable<E> {
        return Zips(
            source1: source1.asObservable(), source2: source2.asObservable(), source3.asObservable(), resultSelector:resultSelector
        )
    }
}