Google c++ style guide forbids default args in virtual functions.
Ashish said he was asked a common question in multiple c++ interviews. The default arg value is “declared” in base class and (or) derived class but never saved in the vtable. It’s basically resolved statically, at compile time.
If you use a pointer to Base to invoke the virtual method, then the Base default arg value applies unconditionally, even though the subclass method is chosen at run time, via the vtable. Highly confusing.