Passing optional callback into Swift function

Question

I\'m learning Swift lang, but I cannot pass optional callback argument into function:

func dismiss(completion: () -> Void) {
    if (completion) {
        ret         


        

Answer 1

It's better to add = nil in the callback declaration, to avoid passing nil while calling it:

func dismiss(completion: (() -> Void)? = nil) {
    if (completion) {
        return self.dismissViewControllerAnimated(true, completion: completion)
    }
    self.dismissModalViewControllerAnimated(true) }

And you can call your function like this : dismiss()