"is" keyword in Swift

Question

As far as I can look, it seems that the consensus is that the is in Swift keyword is synonymous to isKindOfClass method.

However, I'm having trouble getting the following to work:

//inside of a method in UITabViewController

//check if the currently selected tab is ActivityViewController
if selectedViewController is ActivityViewController {
    print("isActivity")
} else {
    print("isNotActivity")
}


//same check
if selectedViewController?.isKindOfClass(ActivityViewController) != nil {
    print("isActivity")
} else {
    print("isNotActivity)
}

When this block of code was called, I made sure I was in my ActivityViewController tab. isKindOfClass was correct, selectedViewController is ActivityViewController was not. Any ideas as to why this is?

Answer 1

is and isKindOfClass are not synonyms, see for example Is there a difference between "is" and isKindOfClass()?.

In your case however, the problem is the optional chaining.

selectedViewController?.isKindOfClass(ActivityViewController)

returns an Optional<Bool> which is nil if the call could not be made (because selectedViewController is nil), and a non-nil value otherwise. So

selectedViewController?.isKindOfClass(ActivityViewController) != nil

is true if the call could be made, independent of whether the return value is true or false.

With

if selectedViewController?.isKindOfClass(ActivityViewController) == true { ... }

you would get the expected result.