Open Radar

 
Summary:
In Obj-C, -[NSJSONSerialization JSONObjectWithData] returns id, and the docs indicate it will be a Foundation type, meaning either NSArray or NSDictionary.

In Swift, this returns arrays or dictionaries of unexpected types that are burdensome to unbundle. Specifically:
1. The object can be cast to Array<Dictionary<String,AnyObject>> (or Dictionary<String,AnyObject>[]), but not Array<Dictionary<String,Any>>.
2. When the value of a given name-value pair in the dictionary is a string, it cannot be cast to a Swift string (this causes a compiler error). It must be retrieved as an AnyObject? and then cast to a Swift String, or retrieved as an NSString.

Steps to Reproduce:
Run the sample project NSJSONSerializationSwiftBuglet. It reads a bundled JSON file as NSData (the results of performing an SLRequest to read a Twitter timeline), uses NSJSONSerialization.JSONObjectWithData to create an AnyObject? called jsonData,  and then attempts various techniques to get at the contents of the JSON object. These techniques log messages to a UITextView.

Expected Results:
The data is an array of dictionaries, which are keyed with strings and can have either arrays, dictionaries, or strings as values… so I would expect to be able to cast to NSArray<NSDictionary<String, Any>>, since the Swift string is not an object, per se.

Actual Results:
Here's the output:
got a jsonObject
----------------
----------------
it's not an Array<Dictionary<String,Any>>
----------------
it's an Array<Dictionary<String,AnyObject>>
 * First Tweet: RT @edbott: No. Just no. RT @ow The future on your wrist http://t.co/ecIs4co62J
    * Roundabout NSString technique works here
----------------
it's a Dictionary<String,AnyObject>[]
  * First Tweet: RT @edbott: No. Just no. RT @ow The future on your wrist http://t.co/ecIs4co62J
    * Roundabout NSString technique works here
----------------
it's an Array<AnyObject>
first object is a Dictionary <String, AnyObject>
  * First Tweet: RT @edbott: No. Just no. RT @ow The future on your wrist http://t.co/ecIs4co62J
    * Roundabout NSString technique works here
----------------
it's not an Array<Any>
no further tests here, I'm lazy
----------------
it's an NSArray
no further tests here, I'm lazy
----------------

Points of interest:

1. I *cannot* cast the jsonObject to  Array<Dictionary<String,Any>>, though I can cast it to  Array<Dictionary<String,AnyObject>>. Why would the more general cast fail, and the more specific cast succeed?

2. I would expect to be able to cast the value of a name-value pair to a string optional ("String?") like this:
    let tweetText : String?  = tweetDict["text"] as? String
however, if the jsonObject was cast to Array<Dictionary<String,AnyObject>>, the compiler rejects this line as "Could not find an overload for 'subscript' that accepts the supplied arguments". OTOH, this line compiles when jsonObject was cast to Array<Dictionary<String,Any>>, but that block never executes anyways.

3. Casting values to NSStrings instead of Swift strings seems to always compile and always work.

Version:
Xcode 6 beta 2, OS X 10.9.3

Notes:
My main complaints are that
1. Casting the jsonObject to Array<Dictionary<String,Any>> is the intuitive choice and should work.
2. In the Array<Dictionary<String,AnyObject>> case, getting the value from the dictionary with "let tweetText : String?  = tweetDict["text"] as? String" is the intuitive way to get a Swift string and should compile (and would, if point 1 were true). The compiler error here is also unhelpful.

Configuration:
Early 2008 Mac Pro

Attachments:
'NSJSONSerializationSwiftBuglet.zip' was successfully uploaded.


OpenRadar readers: buglet code at https://dl.dropboxusercontent.com/u/12216224/buglets/NSJSONSerializationSwiftBuglet.zip