swift：关闭声明就像块声明

在对函数类型的语法是

(in)-> out

typealias CompletionBlock = (NSString?) -> Void// ortypealias CompletionBlock = (result: NSData?, error: NSError?) -> Voidvar completion: CompletionBlock = { reason in print(reason) }var completion: CompletionBlock = { result, error in print(error) }

请注意，从Swift 3+开始，仅需在输入类型周围加上括号。