Swift Array of dictionaries extension sortInPlace -

using swift 2.1 i'm trying make function sorts array of dictionaries date value key datekey.

i want add extension array type, can call using somearray.sortdictionariesbydate(datekey: string, dateformatter: nsdateformatter)

extension array element: collectiontype {   mutating func sortdictionariesbydate(datekey: string, dateformatter: nsdateformatter) {     sortinplace {       dateformatter.dateformat = "yyyy-mm-dd't'hh:mm:ss.sssz"       if let datestringa: string = ($0 as? [string: anyobject])?[datekey] as? string, let datestringb = ($1 as? [string: anyobject])?[datekey] as? string {         if let datea: nsdate = dateformatter.datefromstring(datestringa), dateb: nsdate = dateformatter.datefromstring(datestringb) {           return datea.compare(dateb) == .orderedascending         }       }       return false     }   } } 

this works fine long dictionaries typed [string: anyobject], if use on dictionary of type [string: string] doesn't work since it's unable cast string anyobject. assume because string struct not class. i've tried typecast elements [string: any] instead, won't work regardless of using dictionaries of type [string: anyobject] or [string: string].

is there cast can use support dictionaries key type string , value type (string, anyobject etc.), or perhaps clause or protocol conformance can added extension avoid casting completely?

edit: here 2 example arrays per request

var samplearray1: [[string: anyobject]] = [["date": "2015-10-24t13:00:00.000z", "foo": "bar"], ["date": "2015-10-24t14:00:00.000z", "foo": "bar"]] samplearray1.sortdictionariesbydate("date", dateformatter: nsdateformatter()) var samplearray2: [[string: string]] = [["date": "2015-10-24t13:00:00.000z", "foo": "bar"], ["date": "2015-10-24t14:00:00.000z", "foo": "bar"]] samplearray2.sortdictionariesbydate("date", dateformatter: nsdateformatter()) 

first issue: comparing strings, not dates. fortunately, string's format make directly comparable both string , date value represents. hence, don't need convert nsdate @ all.

the second issue typecasting dictionary<key,value1> dictionary<key,value2> wholesale doesn't work, when value1 covariant on value2. may work in trivial example this...

let : [string: string] = ["name": "david", "location": "chicago"] let b = [string: anyobject] 

...because compiler can see value type (string) in a , optimize compile time. dynamic situations yours, there's no information available ahead of time.

---

when need dynamism, can go old friend, objective-c:

extension array element: collectiontype {     mutating func sortdictionariesbydate(datekey: string) {         self.sortinplace {             if let = $0 as? nsdictionary, b = $1 as? nsdictionary {                 return (a[datekey] as? string) < (b[datekey] as? string)             } else {                 return false             }         }     } }  // example: var samplearray1: [[string: anyobject]] = [     ["date": "2015-10-24t13:00:00.000z", "foo": "bar"],     ["date": "2015-10-24t14:00:00.000z", "foo": "bar"],     ["date": "2015-10-24t10:00:00.000z", "foo": "bar"] ] var samplearray2: [[string: string]] = [     ["date": "2015-10-24t13:00:00.000z", "foo": "bar"],      ["date": "2015-10-24t14:00:00.000z", "foo": "bar"],     ["date": "2015-10-24t10:00:00.000z", "foo": "bar"] ]  samplearray1.sortdictionariesbydate("date") samplearray2.sortdictionariesbydate("date") 

note since comparing strings rather date, no nsdateformatter needed.