JSON Serialization

JSON serialization is essentially unchanged in Swift for one reason: it happens in foundation objects just as it did in Objective-C. Once we get the results back there are slightly different patterns for dealing with the data which we’ll see shortly.

The basics, in Objective-C:

NSData *data = ...some data loaded...;
NSError *jsonError = nil;
NSDictionary *decodedData = [NSJSONSerialization JSONObjectWithData:data options:0 error:&jsonError];
if (!jsonError) {

Lots of boilerplate, but still pretty simple. Now the same, in Swift:

let data: NSData = ...some data loaded...
let jsonError: NSError?
let decodedJson = NSJSONSerialization.JSONObjectWithData(data, options: nil, error: &jsonError!) as Dictionary<String, AnyObject>
if !jsonError {

Yes, just like before when we had to know we were going to get back an NSDictionary from JSONObjectWithData:options:error:, we still have to cast the return from AnyObject to a Dictionary<String, AnyObject> (or whatever type is appropriate). Such are the perils of working with JSON. We could inspect the return type before using it for a more generic case but you’ll probably use the simpler example above when you already know the expected type.

But what! We still have to use & to pass a pointer to the serialization call! This is pretty un-Swifty and I suspect that a future where Apple is using Swift internally will deliver us more Swifty API calls. For now, at least understand that the & here doesn’t actually mean a pointer (there are no pointers in swift), but rather an inout variable. inouts are just markers to let functions know they can modify the parameters being passed in. The style is pretty C-like so I’m curious why it was included in the language, especially since we have multiple return values in Swift (hit us up for ideas on twitter).