How to represent an optional Bool (Bool?) in Objective-C?

The problem is this type declaration:

`isValid: Bool?`

That is perfectly fine in Swift. But you cannot expose it to Objective-C, because Objective-C does not have any notion of an Optional BOOL - a BOOL in Objective-C is basically just a number, a primitive C datatype (what we call a scalar).

Here's another way of looking at it. In an interchange with Objective-C, you can use a Swift Optional anywhere that Objective-C can say nil - indeed, to a large extent Swift Optional exists exactly in order to deal with the possibility that Objective-C will say nil or that you might need to say nil to Objective-C. But a BOOL in Objective-C can never be nil - it can only be YES or NO (Swift true or false).

So you have three choices:

• Take away the @objc that exposes all this to Objective-C

• Remove the Optional and just declare that type a Bool

• Use an object type. For example, declare the type as AnyObject? (or NSNumber?). This will work because Swift will bridge a Bool to an NSNumber (including as it passes into an AnyObject), and Objective-C will deal just fine with an Optional AnyObject or Optional NSNumber because those are object types, not scalars.

Object-C does not have the concept of optionals, try to remove the "?" from your declaration