No we should not support enum types derived from strings

[deadalnix]

On Wednesday, 12 May 2021 at 11:41:20 UTC, Andrei Alexandrescu 
wrote:
> On 5/11/21 9:46 PM, deadalnix wrote:
>> This whole model in C++ is unsound. It's easy to show. In you 
>> above example, the this pointer, typed as Widget*, points to 
>> an instance of a subclass of Widget. If you were to assign a 
>> Widget to that pointer (which you can do, this is a pointer to 
>> a mutable widget), then any references to that widget using a 
>> subtype of Widget is now invalid.
>
> All of this is bizarrely incorrect. Care to elaborate?

Consider the following: https://godbolt.org/z/8vzx9W56a

This is a clear demonstration that C++'s type system is unsound 
here.

It is unsound because it has the property that you mentioned in 
your post: the pointer is monomorphic and the value this pointers 
points to is polymorphic. This is simply unsound, you cannot 
separate the two (unless you make everything immutable).

The pointer and the value must come together as a bundle, and 
that whole bundle (which is a value type containing a reference) 
is itself what is polymorphic. That's what Java/C#/D do and this 
is right.