How do I port a "virtual" method from a c++ base class?

The project I’m working on borrows some logic from c++ code. In several places that code declares “virtual” methods in a base class then only some derived classes implement the method.

How can I “port” this logic to my code?

All methods in Xojo are virtual ones and can be overwritten.

I suspected that, but does this mean I can just declare a method with no implementation of it in the base class/.

Just define methods in both classes with same signatures.