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

Just adding to Martin R's answer above..

The callback can be optional, instead of implicit parameter (with exclamation mark), use the optional operator.

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

    self.dismissModalViewControllerAnimated(true)
}