How to use inheritance when interfacing with C++ classes?

[Tim]

On Thursday, 9 December 2021 at 19:05:08 UTC, rempas wrote:
> Anyone has an idea?

The referenced methods like Fl_Widget::_clear_fullscreen are 
implemented directly in the header, so the D code also needs the 
implementation, because it is not included in the compiled 
library.

Methods, which are not virtual in C++, also have to be marked 
final in D, because C++ and D use a different default.