swift - How do you sort dates in a dictionary? -

i having trouble trying sort following dictionary, printed in oldest date first order when printed.

var daytotaldictest: [string:int] =              [                 "04-09-2015" : 4,                 "04-10-2015" : 6,                 "04-07-2015" : 8,                 "03-28-2015" : 10,                 "12-10-2014" : 12,                 "12-10-2015" : 12,              ] 

edit/update: xcode 8.2.1 • swift 3.0.2

extension string {     static let shortdateus: dateformatter = {         let formatter = dateformatter()         formatter.calendar = calendar(identifier: .iso8601)         formatter.locale = locale(identifier: "en_us_posix")         formatter.datestyle = .short         return formatter     }()     var shortdateus: date? {         return string.shortdateus.date(from: self)     } }  let daytotaldictest: [string:int] = [     "04-09-2015" : 4,     "04-10-2015" : 6,     "04-07-2015" : 8,     "03-28-2015" : 10,     "12-10-2014" : 12,     "12-10-2015" : 12]  let myarrayoftuples = daytotaldictest.sorted{     guard let d1 = $0.key.shortdateus, let d2 = $1.key.shortdateus else { return false }     return d1 < d2 }  print(myarrayoftuples)  // [("12-10-2014", 12), ("03-28-2015", 10), ("04-07-2015", 8), ("04-09-2015", 4), ("04-10-2015", 6), ("12-10-2015", 12)]\n"  tuple in myarrayoftuples {     print(tuple) }