如何在 Swift 3 中将 __NSMallocBlock__ 转换为其基础类型？

I had a trick帮助测试UIAlertController在 Swift 2.x 中有效：

extension UIAlertController {

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

    func tapButtonAtIndex(index: Int) {
        let block = actions[index].valueForKey("handler")
        let handler = unsafeBitCast(block, AlertHandler.self)

        handler(actions[index])
    }

}

这在 Swift 3.x 下失败了fatal error: can't unsafeBitCast between types of different sizes，这让我相信可能有办法让演员阵容发挥作用。有人能弄清楚吗？

找到了适用于 Swift 3.0.1 的解决方案

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<AnyObject>.passUnretained(block as AnyObject).toOpaque())
            let handler = unsafeBitCast(blockPtr, to: AlertHandler.self)
            handler(actions[index])
        }
    }

}

（原本，blockvalue 是实际的块，而不是指向块的指针——显然你不能将其转换为指向的指针AlertHandler)