No we should not support enum types derived from strings

[Andrei Alexandrescu]

On 5/12/21 8:11 AM, deadalnix wrote:
> 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.

Ah, now we're at slicing. Love these forum discussions!