Why is D unpopular

[Ola Fosheim Grøstad]

On Monday, 13 June 2022 at 10:55:36 UTC, Ola Fosheim Grøstad 
wrote:
> On Monday, 13 June 2022 at 10:51:10 UTC, Mike Parker wrote:
>> And I'm arguing that this is exactly what we should expect 
>> from private-to-the-module, since B is not declared in the 
>> same module as the superclass, so it's neither unfinished nor 
>> a bug.
>
> It breaks the sub-typing requirement.
>
> If you get more access by recasting a pointer to the super-type 
> then the sub-typing relation cannot be satisfied.
>
> Hence, it is certainly broken. If it is not a bug, then it is 
> broken by design. Which is no better.

Or to explain it in simple terms:

*A cast to a supertype should only imply additional restrictions.*

In this case the opposite happens. So this aspect of the type 
system is broken.