T.init, struct destructors and invariants - should they be called?

[FeepingCreature]

On Tuesday, 10 July 2018 at 00:01:28 UTC, Steven Schveighoffer 
wrote:
> On 7/7/18 11:06 PM, FeepingCreature wrote:
>> On Friday, 6 July 2018 at 23:37:30 UTC, Simen Kjærås wrote:
>>> As for alignment, GC, and possibly other things, the code was 
>>> not intended as a complete implementation of Nullable, only 
>>> to show that an actual member of type T is not necessary. 
>>> These issues are fixable, if perhaps nontrivial in some cases.
>>>
>>> --
>> 
>> Yeah, sorry - that was a snap answer; union is indeed not a 
>> solution, particularly since it doesn't even work for types 
>> with elaborate destructors.
>> 
>> That said, I agree that this can be implemented, however imo 
>> the fact that we have to retrace the work of the compiler in 
>> laying out the data is a warning sign - imo, it happens 
>> because what we actually want is for the compiler to *work a 
>> different way*, which is why we find ourselves painstakingly 
>> recreating its interna in userland, except with different 
>> destructor semantics. This points at a flaw in the language, 
>> imo - if we so urgently need a way to express different 
>> semantics, we shouldn't have to painstakingly hide the type 
>> behind the compiler's back; the compiler should have our back 
>> in this instead of fighting us.
>
> Hm... this reminds me of the recent discussion around 
> __symbols, and how they are treated specially.
>
> Could we reserve some subset of those symbols to say "treat 
> these differently"?
>
> Or have an attribute that marks a member in such a way? I'm 
> reminded of of the future storage class __mutable as well.
>
> -Steve

That would also solve the problem.

Note that I've recently realized that the format!"" 
weird-exception bug ( issue 19003 
https://issues.dlang.org/show_bug.cgi?id=19003 ) is based on the 
same root assumption - Phobos blithely presumes that T.init is a 
valid instance of T that it can, say, call toString() on.

Do you think "Structs with nontrivial Domain Data Considered 
Harmful" would make a good article name?