Comparator.swift

import Foundation

extension Collection where Element: Comparable {    
    func sorted(ascending: Bool = true, using comparator: (Element) -> (Element) -> ComparisonResult) -> [Element] {
        return self.sorted { lhs, rhs in
            comparator(lhs)(rhs) == (ascending ? .orderedAscending : .orderedDescending)
        }
    }
}

let words = ["whisky", "tango", "foxtrot"]
words.sorted(using: String.localizedStandardCompare)
// => ["foxtrot", "tango", "whisky"]