Create an optional block as a variable
The way you have written it, the compiler assumes progressBlock is a closure that returns an optional empty tuple instead of an optional closure that returns an empty tuple. Try writing it like this instead:
class MyObject:NSObject { var progressBlock:((progress:Double) -> ())? init() { progressBlock = nil progressBlock = { (Double) -> () in /* code */ } }}
Adding to connor's reply. An optional block can be written as:
var block : (() -> ())? = nilOr as an explicit Optional:
var block : Optional<() -> ()> = nilOr better yet, with a custom type
typealias BlockType = () -> ()var block : BlockType? = nil