zip运算符

该运算符的作用可以用下面的图片描述：

屏幕快照 2016-03-12 下午5.59.52.png

下面是代码实现：

class ZipObserver<ElementType>: ObserverType, LockOwnerType, SynchronizedOnType {
    typealias E = ElementType
    typealias ValueSetter = (ElementType)->()

    private var _parent: ZipSinkProtocol?
    let _lock: NSRecursiveLock

    // state
    private let _index: Int
    private let _this: Disposable
    private let _setNextValue: ValueSetter
    init(lock: NSRecursiveLock, parent: ZipSinkProtocol, index: Int, setNextValue: ValueSetter, this: Disposable) {
        _lock = lock
        _parent = parent
        _index = index
        _this = this
        _setNextValue = setNextValue
    }

    func on(event: Event<E>) {
        synchronizedOn(event)
    }

    func _synchronized_on(event: Event<E>) {
        if let _ = _parent {
            switch event {
            case .Next(_):
                break
            case .Error(_):
                _this.dispose()
            case .Completed:
                _this.dispose()
            }
        }

        if let parent = _parent {
            switch event {
            case .Next(let value):
                _setNextValue(value)
                parent.next(_index)
            case .Error(let error)
                parent.fail(error)
            case .Completed:
                parent.done(_index)
            }
        }
    }
}

protocol ZipSinkProtocol : class {
    func next(index: Int)
    func fail(error: ErrorType)
    func done(index: Int)
}

class ZipSink<O: ObserverType> : Sink<O>, ZipSinkProtocol {
    typealias Element = O.E

    let _arity: Int
    let _lock = NSRecursiveLock()

    // state
    private var _isDone: [Bool]

    init(arity: Int, observer: O) {
        _isDone = [Bool](count: arity, repeatedValue: false)
        _arity = arity
        
        super.init(observer: observer)
    }

    func getResult() throws -> Element {
        abstractMethod()
    }

    func hasElements(index: Int)->Bool {
        abstractMethod()
    }

    func next(index: Int) {
        var hasValueAll = true
        for i in 0..< _arity {
            if !hasElements(!) {
                hasValueAll = false
                break
            }
        }

        if hasValueAll {
            do {
                let result = try getResult()
                self.forwardOn(.Next(result))
            }catch let e {
                self.forwardOn(.Error(e))
                dispose()
            }
        }else {
            var allOthersDone = true
            
            let arity = _isDone.count
            for i in 0..< arity {
                if i != index && !_isDone[i] {
                    allOthersDone = false
                    break
                }
            }

            if allOthersDone {
                forwardOn(.Completed)
                self.dispose()
            }
        }
    }

    func fail(error: ErrorType) {
        forwardOn(.Error(error))
        dispose()
    }

    func done(index: Int) {
        _isDone[index] = true

        var allDone = true

        for done in _isDone {
            if !done {
                allDone = false
                break
            }
        }

        if allDone {
            forwardOn(.Completed)
            dispose()
        }
    }
}