Repository: ReactiveX/RxSwift
File: RxSwift/Observables/TakeUntil.swift (Swift)

Code before:
//
//  TakeUntil.swift
//  RxSwift
//
//  Created by Krunoslav Zaher on 6/7/15.
//  Copyright © 2015 Krunoslav Zaher. All rights reserved.
//

extension ObservableType {

    /**
     Returns the elements from the source observable sequence until the other observable sequence produces an element.

     - seealso: [takeUntil operator on reactivex.io](http://reactivex.io/documentation/operators/takeuntil.html)

     - parameter other: Observable sequence that terminates propagation of elements of the source sequence.
     - returns: An observable sequence containing the elements of the source sequence up to the point the other sequence interrupted further propagation.
     */
    public func takeUntil<O: ObservableType>(_ other: O)
        -> Observable<E> {
        return TakeUntil(source: self.asObservable(), other: other.asObservable())
    }
}

final fileprivate class TakeUntilSinkOther<Other, O: ObserverType>
    : ObserverType
    , LockOwnerType
    , SynchronizedOnType {
    typealias Parent = TakeUntilSink<Other, O>
    typealias E = Other
    
    fileprivate let _parent: Parent

    var _lock: RecursiveLock {
        return _parent._lock
    }
    
    fileprivate let _subscription = SingleAssignmentDisposable()
    
    init(parent: Parent) {
        _parent = parent
#if TRACE_RESOURCES
        let _ = Resources.incrementTotal()
#endif
    }
    
    func on(_ event: Event<E>) {
        synchronizedOn(event)
    }

    func _synchronized_on(_ event: Event<E>) {
        switch event {
        case .next:
            _parent.forwardOn(.completed)
            _parent.dispose()
        case .error(let e):
            _parent.forwardOn(.error(e))
            _parent.dispose()
        case .completed:
            _subscription.dispose()
        }
    }
    
#if TRACE_RESOURCES
    deinit {
        let _ = Resources.decrementTotal()
    }
#endif
}

final fileprivate class TakeUntilSink<Other, O: ObserverType>
    : Sink<O>
    , LockOwnerType
    , ObserverType
    , SynchronizedOnType {
    typealias E = O.E
    typealias Parent = TakeUntil<E, Other>
    
    fileprivate let _parent: Parent
 
    let _lock = RecursiveLock()
    
    
    init(parent: Parent, observer: O, cancel: Cancelable) {
        _parent = parent
        super.init(observer: observer, cancel: cancel)
    }
    
    func on(_ event: Event<E>) {
        synchronizedOn(event)
    }

    func _synchronized_on(_ event: Event<E>) {
        switch event {
        case .next:
            forwardOn(event)
        case .error:
            forwardOn(event)
            dispose()
        case .completed:
            forwardOn(event)
            dispose()
        }
    }
    
    func run() -> Disposable {
        let otherObserver = TakeUntilSinkOther(parent: self)
        let otherSubscription = _parent._other.subscribe(otherObserver)
        otherObserver._subscription.setDisposable(otherSubscription)
        let sourceSubscription = _parent._source.subscribe(self)
        
        return Disposables.create(sourceSubscription, otherObserver._subscription)
    }
}

final fileprivate class TakeUntil<Element, Other>: Producer<Element> {
    
    fileprivate let _source: Observable<Element>
    fileprivate let _other: Observable<Other>
    
    init(source: Observable<Element>, other: Observable<Other>) {
        _source = source
        _other = other
    }
    
    override func run<O : ObserverType>(_ observer: O, cancel: Cancelable) -> (sink: Disposable, subscription: Disposable) where O.E == Element {
        let sink = TakeUntilSink(parent: self, observer: observer, cancel: cancel)
        let subscription = sink.run()
        return (sink: sink, subscription: subscription)
    }
}


Review comment (suggestion):
I would probably put `self` everywhere. I know that we weren't consistent in the past, but looks good enough to pull in.

Code after:
    
    override func run<O : ObserverType>(_ observer: O, cancel: Cancelable) -> (sink: Disposable, subscription: Disposable) where O.E == Element {
        let sink = TakeUntilSink(parent: self, observer: observer, cancel: cancel)
        let subscription = sink.run()
        return (sink: sink, subscription: subscription)
    }
}

// MARK: - TakeUntil Predicate
final fileprivate class TakeUntilPredicateSink<O: ObserverType>
    : Sink<O>, ObserverType {
    typealias Element = O.E
    typealias Parent = TakeUntilPredicate<Element>

    fileprivate let _parent: Parent
    fileprivate var _running = true

    init(parent: Parent, observer: O, cancel: Cancelable) {
        _parent = parent
        super.init(observer: observer, cancel: cancel)
    }

    func on(_ event: Event<Element>) {
        switch event {
        case .next(let value):
            if !_running {
                return
            }

            do {
                _running = try !_parent._predicate(value)
            } catch let e {
                forwardOn(.error(e))
                dispose()
                return
            }

            if _running {
                forwardOn(.next(value))
            } else {
                if _parent._behavior == .inclusive {
                    forwardOn(.next(value))
                }

                forwardOn(.completed)
                dispose()
            }
        case .error, .completed:
            forwardOn(event)
            dispose()
        }