On Tue, Apr 15, 2025 at 5:41 PM Jason McKesson wrote:
>
> If you want your concept to be extensible, for types to explicitly
> opt-in, you can.


I think you're talking about tags.

class MyClass {
public:
    typedef int IsArithmetic;
};

And I think maybe tags should be standardised, the default behaviour
being that a tag is inherited by derived classes unless you mark it
"final" as follows:

class MyClass {
public:
    _Tag IsArithmetic : final; // This one is not inherited by derived classes
    _Tag IsNuclear; // This one is inherited by derived classes
};