Completion handler with nil value

Question

I would like to create a function with completion handler and I would like to make the handler so I can pass in nil.

func animate(completion: @escaping((Bool) -> ()) {
  //Do stuff
  completion(true)
}

I would like make the make the completion handler to be able to pass in nil when it's not needed, like:

animate(completion: nil)

It's not working & I get the error:

Nil is not compatible with expected argument type '(Bool?) -> ()

. Can you please help me how to do this?

closure in function arguments swift can be treated as any other argument type and hence can be made optional. — Puneet Sharma, Dec 21 '17 at 10:27

Hexfire · Answer 1 · 2017-12-21T10:32:11.780

Remove @escaping keyword and make closure optional by specifying default value. Note that this way optional closure de-facto remains escaping.

func animate(_ completion: ((Bool) -> ())? = nil) {
    //Do stuff
    completion?(true)
}

Possible usages:

animate({ value in
    print("Completion value: \(value)")
})
animate(nil)
animate() // pass nothing, because default value is nil

As trailing closure:

animate() { value in
    print("Completion value: \(value)")
}

1 Answers1