Dynamic templated virtuals - I still often want them

[Adam D. Ruppe]

On Thursday, 23 July 2020 at 16:06:03 UTC, Steven Schveighoffer 
wrote:
> Potentially as well, you could specify overrides of the Base 
> template in a derived type if needed.

Right, I'd want to do that with a normal `override` definition 
just like any other method.

(semantically, the virtual template would probably work the same 
as a mixin template. If you provide your own override, it just 
ignores the template version using yours instead.)

> One other tricky thing is that the override functions must not 
> vary the parameter or return types (except for covariance).

Yeah, it would still be subject to the same semantic checks as if 
it was written by hand and would need to error there; it is still 
an interface method. Though the compiler might not actually 
diagnose that error until you actually try to subclass it (again, 
just like the mixin template thing, just without the explicit 
`mixin X`).