Xcode closure auto completion issue

Question

The following is working code built against iOS 8.4 using Xcode 6.4

NSURLConnection.sendAsynchronousRequest(urlRequest, queue: NSOperationQueue.mainQueue(), completionHandler: { response, data, error in
    if error != nil {
        println("there be an error")
    } else {
        let image = UIImage(data:data)
        self.webimage.image = image
    }
})

If I double click the closure section of the method signature as Xcode auto completes it I end up in this state:

Xcode has not put }) at the end of the closure and also added -> Void in .

Is this a bug in Xcode 6.4 or are there two alternate syntaxes for closures?

When would I need completionHandler : { arg, arg arg in versus completionHandler : {(arg,arg,arg) -> Void in //code })

Answer 1

The way that Xcode autocomplete your instruction is in the "trailing closures style."

From the Apple documentation:

If you need to pass a closure expression to a function as the function's final argument and the closure expression is long, it can be useful to write it as a trailing closure instead. A trailing closure is a closure expression that is written outside of (and after) the parentheses of the function call it supports

If you want to know more about the trailing closure, please report to the doc here: https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Closures.html (cf section Trailing Closures)