This was particularly interesting to me due to the &error addressing and the use of “as?” to test the error. I’m in a bit of a rush right now so I apologize for the brevity of the explanation. I’ll try to fill it out more later when I have some time.

func DataFromURL(url : NSURL) -> (NSData?)
{
    var error : NSError? = nil
    let data : NSData? = NSData.dataWithContentsOfURL(
        url, options: NSDataReadingOptions.fromMask(0), error: &error)
    if (data == nil)
    {
        if let theError = error as? NSError
        {
            let reason : String? = theError.localizedDescription
            println("Error reading from URL \(url) : \(reason)")
            return nil
        }
    }
    return data
}

func DataFromURL(urlString : NSString) -> (NSData?)
{
    var url = NSURL(string: urlString)
    let standard = url.resourceSpecifier.hasPrefix("//")
    
    if (!standard)
    {
        url = NSURL(fileURLWithPath: urlString)
    }

    if (url === nil) {return nil}
    return DataFromURL(url)
}

In this one, I needed to get a void * to pass for the key, again leading to an interesting solution. By the way, I haven’t debugged the actual  associated object stuff (I’ll update this when I do) so please just note the CConstVoidPointer bit. (Update: it all seems to be working in my tests.)

var sharedObserverSelector : Selector = "observers"
var sharedObserversKey : CConstVoidPointer = &sharedObserverSelector

extension UIViewController
{
    func setObservers(array : NSMutableArray)
    {
        objc_setAssociatedObject(self, sharedObserversKey, array, UInt(OBJC_ASSOCIATION_RETAIN_NONATOMIC))
    }
    
    func observers() -> (NSMutableArray)
    {
        let object : AnyObject? = objc_getAssociatedObject(self, sharedObserversKey)
        if (object === nil)
        {
            let array = NSMutableArray()
            self.setObservers(array)
            return array
        }
        return object as NSMutableArray
    }