Swift NSMutableDictionary parsing json fails

I have some weird parsing problems with NSMutableDictionary and Alamofire json response.

Alamofire.request(.POST, "\(Constants.apiUrl)/get_stuff", parameters: mapData, encoding:.JSON)
    .responseJSON { response in

        switch response.result {
        case .Success(let data):
            let info = data as! NSMutableDictionary

            self.deleteCategoryFromCoreData()

            if let categoryArray = info["category"] as? NSArray{
                for var i = 0; i < categoryArray.count; i++ {
                    self.categoryID = categoryArray[i]["id"] as? Int  <-- error here
                    self.categoryName = categoryArray[i]["name"] as? NSString
                    self.saveCategoryDataToCoreData()
                }
            }

I dont know why this fails:

(lldb) po categoryArray[i]["id"]
2016-05-23 20:59:56.892 MyProject[9799:5005782] -[__NSCFNumber length]: unrecognized selector sent to instance 0xb000000000000013
error: Execution was interrupted, reason: internal ObjC exception breakpoint(-3)..
The process has been returned to the state before expression evaluation.

but this does not fail:

(lldb) po categoryArray[i]["name"]
▿ Optional<String>
  - Some : "Animals"

Here is the data:

(lldb) po categoryArray[i]
▿ 2 elements
  ▿ [0] : 2 elements
    - .0 : id
  ▿ [1] : 2 elements
    - .0 : name
    - .1 : Animals

Why can't I access "id" key ? I cant parse json like this? I was told to try SwiftyJSON, this way not possible at all. All this problem happened after I updated to Xcode 7.3 and cocoapods 1.0.0.

Foundation collection types don't contain type information and the mutable versions NSMutableArray and NSMutableDictionary aren't related to the Swift counterparts at all.

Use Swift native types for everything

Alamofire.request(.POST, "\(Constants.apiUrl)/get_stuff", parameters: mapData, encoding:.JSON)
  .responseJSON { response in

    switch response.result {
    case .Success(let data):
      let info = data as! [String:AnyObject]

      self.deleteCategoryFromCoreData()

      if let categoryArray = info["category"] as? [[String:AnyObject]] {
        for category in categoryArray {
          self.categoryID = category["id"] as? Int
          self.categoryName = category["name"] as? String
          self.saveCategoryDataToCoreData()
        }
      }

If you still get the error than the value for key id is a string

if let id = category["id"] as? String {  
   self.categoryID = Int(id)
}

PS: Consider that you assign all values in the repeat loop to the same variables categoryID and categoryName respectively, that means the value will be overwritten in each iteration.