Cannot convert value of type '(_) -> ()?' to expected argument type '@convention(block) () -> Void'

Question

This piece of code ran fine in Swift 3, but now after conversion of code by the Xcode into Swift 4, it is throwing error. I am presenting the next scene in the main queue, based on the values I got from the web-service.

DispatchQueue.main.async {
    [weak self] value in
    self?.router?.invokeTheSegueAfterTheWebService(navigationKey: arrayElementsGot["questionType"] as! String, givenViewController: self!)
}

Answer 1

In Swift 3, the value parameter was inferred to have the type () .

Swift 4 no longer allows you to provide a single parameter to blocks that contextually should take a different number of parameters. So your code should look like

DispatchQueue.main.async {
    [weak self] in
    self?.router?.invokeTheSegueAfterTheWebService(navigationKey: arrayElementsGot["questionType"] as! String, givenViewController: self!)
}

If you look at the error you got, it says that it expected () -> Void (eg a block with no parameters) but you passed it (_) -> () (eg a block with one parameter of unknown type).