Swift 闭包与AnyObject的互转

在习惯了原来的OC开发，可能将多个block做为函数参数，亦或是存入集合类型（NSDictionary、NSArray）的实例中，但在Swift中将闭包存入一个Dictionary或Array中是不行的。其解决方案是用 unsafeBitCast 函数将Swift闭包转为Objective-C的兼容的对象，如下：

//使用`@convention(block)` 关键字，Swift2.0以后@objc_block属性由@convention(block)取代。
typealias CompletionBlock = @convention(block) () -> Void

        let aBlock:CompletionBlock = {
            print("Hello world!")
        }
        let nsArray = NSMutableArray()
        let blockObject = unsafeBitCast(aBlock, AnyObject.self)
        nsArray.addObject(blockObject)
        
        let closureObject = nsArray[0]
        let closure = unsafeBitCast(closureObject, CompletionBlock.self)
        closure()