How do I cast an __NSMallocBlock__ to its underlying type in Swift 3?

Question

I had a trick to help test UIAlertController that worked in Swift 2.x:

extension UIAlertController {

    typealias AlertHandler = @convention(b         


        

Answer 1

Found a solution that works in Swift 3.0.1

extension UIAlertController {

    typealias AlertHandler = @convention(block) (UIAlertAction) -> Void

    func tapButton(atIndex index: Int) {
        if let block = actions[index].value(forKey: "handler") {
            let blockPtr = UnsafeRawPointer(Unmanaged.passUnretained(block as AnyObject).toOpaque())
            let handler = unsafeBitCast(blockPtr, to: AlertHandler.self)
            handler(actions[index])
        }
    }

}

(Originally, the block value was the actual block, not a pointer to the block—which you obviously can't cast to a pointer to AlertHandler)