ObjectiveCToSwift.swift

...

@objc(Factory)
internal class Factory: NSObject {
    private static var privateClassType: MyPrivateClass.Type!

    @objc static func registerPrivateClassType(type: MyPrivateClass.Type) {
        print("REGISTRATION CALLED WITH TYPE = \(type)")
        privateClassType = type
    }

    func createMyPrivateClass() -> MyPrivateClass {
        print("FACTORY METHOD CALLED TO CREATE INSTANCE OF \(String(describing: Factory.privateClassType))")
        return Factory.privateClassType.init()
    }
}