extension Array {
    func sortedBy<T: Comparable>(_ cb: (Element) -> T) -> [Element] {
        return self.sorted(by: { (l: Element, r: Element) -> Bool in
            return cb(l) < cb(r)
        })
    }

    func sortedByDescending<T: Comparable>(_ cb: (Element) -> T) -> [Element] {
        return self.sorted(by: { (l: Element, r: Element) -> Bool in
            return cb(l) > cb(r)
        })
    }
}