> If you want to limit what classes can use a class as a base, make everything (esp. constructors) in the class private, make the "welcome" classes friends and ensure that they behave. That's what some of us have indeed been doing for many years in order to limit the set of classes that can inherit from a particular base, and suggestions for some more direct facility haven't come up, because that was unnecessary.
This way you disallow instantiation of a class, not the inheritance itself.
My proposal is about conditionally disallowing inheritance, not instantiation of a class.
If you can do what this proposal proposes, share your knowledge with the community, please.
And the quoted recipe is invalid as it does not do what this proposal proposes (it does not disallow inheritance at all).
[Note you can inherit from a class with all six special member functions explicitly deleted. — end note].
On Tue, 14 Jul 2020 at 11:57, Paweł Benetkiewicz via Std-Proposals
<std-proposals@lists.isocpp.org> wrote:
> > So the basic question "why is this worth having?" is not answered by the proposal.
> The Proposal is worth having, because it does "heavily increase compatibility correctness by inheritance constraints" by providing an ability to encapsulate interfaces. [Note: See Examples section of proposal. — end note]
I can already do what this proposal proposes. There are existing ways
in C++ to reach the same goal, so
the proposal should explain why those ways are inadequate, and why an
extension is necessary.