Custom RxSwift operators

cachePrevious.swift

func cachePrevious<E>(source: Observable<E>) -> Observable<(E?, E)> {
    var previous: E?
    return source >- map {
        let pre = previous
        previous = $0
        return (pre, $0)
    }
}

flatMapEarliest.swift

func flatMapEarliest<E, R>(transform: E -> Observable<R>) -> Observable<E> -> Observable<R> {
    return { source in
        var acceptNew = true

        return source >- flatMap { (n: E) in
            if !acceptNew {
                return empty()
            }

            acceptNew = false

            return create { o in
                let subscription = transform(n)
                    >- subscribe { e in
                        return send(o, e)
                    }

                return AnonymousDisposable {
                    subscription.dispose()
                    acceptNew = true
                }
            }
        }
    }
}

flatMapLatest.swift

func flatMapLatest<E, R>(selector: E -> Observable<R>) -> Observable<E> -> Observable<R> {
    return { $0 >- map(selector) >- switchLatest }
}