Mentioning the required standard in API docs (was: Re: KF5 modules development branches now build in C++17 mode)

[Friedrich W. H. Kossebau]

Am Sonntag, 20. Juni 2021, 12:16:33 CEST schrieb Friedrich W. H. Kossebau:
> As KF5 promises ABI & source backwards-compatibility for the KF5 series to
> its consumers, public KF headers need to stay compatible with projects
> using C++11 (or C++14).
> So in public headers C++17 features can only be used for new API and also
> needs to be guarded properly by respective preprocessor macros to not be
> seen in C++<17 usages of KF headers.

On a related note, we also need to think about how to mark C++17-only features 
(or any counterparts) in the KF API documentation, so developers know from 
first read on whether some KF API fits their project standards. Something like
"C++17 only", " etc. Myself I do not know some good examples in other 
documentation right now to copy from, but definitely IMHO we should provide 
this in ours.

A first related TODO note has been created here:
https://invent.kde.org/frameworks/kapidox/-/issues/7

If you have proposals for how to do that or examples in other existing 
documentation to copy from, please add a note there.

Cheers
Friedrich