CTFE limitation on reinterpreting cast

[Rambutan]

On Wednesday, 30 September 2026 at 00:17:25 UTC, Walter Bright 
wrote:
> On 9/28/2026 3:50 PM, Rambutan wrote:
>> struct B {}
>> struct C {}
>> 
>> __gshared B Bobj;
>> 
>> auto ptr = cast(C*)&Bobj;
>
> CTFE does not do anything that is not memory safe. Consider:
>
> ```d
> struct B { int b; }
> struct C { long c; }
>
> __gshared B Bobj;
>
> auto ptr = cast(C*)&Bobj;
> ```

Thank you for confirming what I speculated earlier in this thread 
when I said this is dangerous and so may be the motive for 
banning reinterpreting casts in CTFE.

However I also pointed out that there is no problem with such a 
cast if the new pointer is never indirected in any way at compile 
time. So a better rule would be to ban any kind of indirection 
using the result of a reinterpreting cast, and NOT to ban the 
cast itself.

That way placing cast pointers to globals in global struct 
initializers would be legal, as it is in C.