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

[rempas]

On Thursday, 9 December 2021 at 21:35:14 UTC, Tim wrote:
>
> 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.

What is funny about that is that I looked an the official class 
reference and copy pasted the code from here but I also looked at 
the header files and saw what you said but for some reason it 
completely slipped from my head...

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

Is this a must or just good practices?