composable.swift

func identity<T>(value: T) -> T {
    return value
}

extension UIImageView {
    func composable_setResizedImage(processUrl proccessUrl: (NSURL -> NSURL) = identity, processImage: (UIImage -> UIImage) = identity) -> NSURL -> Void {
        return { url in
            let processedURL = proccessUrl(url)
            let request = requestForImageUrl(processedURL)
            fetchData(request) { data in
                guard let image = imageFromResponseData(data) else {
                    return
                }
                let processedImage = processImage(image)
                dispatch_async(dispatch_get_main_queue(), {
                    applyImage(processedImage, to: self)
                })
            }
        }
    }

    func downloadAndResizeLocally(url: NSURL) {
        let download = composable_setResizedImage(processImage: resizeImage(to: frame.size))
        download(url)
    }

}