Swift class that instantiates and caches NSDateFormatter objects

CachedDateFormatter.swift

class CachedDateFormatter {
    static let sharedInstance = CachedDateFormatter()
    var cachedDateFormatters = [String: NSDateFormatter]()

    func formatterWith(#format: String, timeZone: NSTimeZone = NSTimeZone.localTimeZone(), locale: NSLocale = NSLocale(localeIdentifier: "en_US")) -> NSDateFormatter {
        let key = "\(format.hashValue)\(timeZone.hashValue)\(locale.hashValue)"

        if let cachedDateFormatter = cachedDateFormatters[key] {
            return cachedDateFormatter
        }
        else {
            let newDateFormatter = NSDateFormatter()
            newDateFormatter.dateFormat = format
            newDateFormatter.timeZone = timeZone
            newDateFormatter.locale = locale
            cachedDateFormatters[key] = newDateFormatter
            return newDateFormatter
        }
    }
}

In my opinion, to have better localized results, you should change line 13 to

      newDateFormatter.dateFormat = NSDateFormatter.dateFormatFromTemplate(format, options: 0, locale: currentLocale)

so format will adapt to country (example is month difference between UK and US)