rx.swift

func rx_setResizedImage(withURL url: NSURL) -> Disposable {
    let backgroundScheduler = ConcurrentDispatchQueueScheduler(globalConcurrentQueueQOS: .Default)
    let mainScheduler = MainScheduler.instance

    return Observable
        .just(url)
        .observeOn(backgroundScheduler)
        .map(photonize(forSize: frame.size))
        .map(requestForImageUrl)
        .flatMap(rx_fetchData)
        .observeOn(backgroundScheduler)
        .map(imageFromResponseData)
        .flatMap(unwrapOptional(ImageDownloadError.NilImage))
        .observeOn(mainScheduler)
        .subscribeNext(applyImage(to: self))
}

func rx2_setResizedImage(withURL url: NSURL) -> Disposable {
    let backgroundScheduler = ConcurrentDispatchQueueScheduler(globalConcurrentQueueQOS: .Default)
    let mainScheduler = MainScheduler.instance

    let request = Observable
        .just(url)
        .observeOn(backgroundScheduler)
        .map(photonize(forSize: frame.size))
        .map(requestForImageUrl)

    let image = request
        .flatMap(rx_fetchData)
        .observeOn(backgroundScheduler)
        .map(imageFromResponseData)
        .flatMap(unwrapOptional(ImageDownloadError.NilImage))

    return image
        .observeOn(mainScheduler)
        .subscribeNext(applyImage(to: self))
}