Is it possible to implement the behavior of an open class or method without using the open modifier?

In Swift, to allow a class or method to be overridden outside the module, you need to use the open modifier. Without open, a class and its methods are by default internal and final for inheritance outside the module. Within the same module, you can use the public modifier for classes and methods, and they will be accessible for inheritance and overriding within that module, but not outside. Therefore, without open, it is not possible to implement the behavior of an open class or method for use outside the module. If the scope is within a single module, then public allows inheritance and overriding without open.