Cast closures/blocks

Question

In Objective-C, I often pass around blocks. I use them very often to implement patterns that help avoid storing stuff into instance variables, thus avoiding threading/timing

Answer 1

I like GoZoner's solution - wrap the block in a custom class - but since you asked for the actual "Swift way" to perform the cast between a block and an AnyObject, I'll just give the answer to that question: cast with unsafeBitCast. (I'm guessing that this is more or less the same as Bryan Chen's reinterpretCast, which no longer exists.)

So, in my own code:

typealias MyDownloaderCompletionHandler = @objc_block (NSURL!) -> ()

Note: in Swift 2, this would be:

typealias MyDownloaderCompletionHandler = @convention(block) (NSURL!) -> ()

Here's the cast in one direction:

// ... cast from block to AnyObject
let ch : MyDownloaderCompletionHandler = // a completion handler closure
let ch2 : AnyObject = unsafeBitCast(ch, AnyObject.self)

Here's the cast back in the other direction:

// ... cast from AnyObject to block
let ch = // the AnyObject
let ch2 = unsafeBitCast(ch, MyDownloaderCompletionHandler.self)
// and now we can call it
ch2(url)