Please fix `.init` property

[Iain Buclaw]

On Tuesday, 9 January 2024 at 06:16:42 UTC, FeepingCreature wrote:
>
> Yes, the point of making it forced `immutable` is exactly to 
> make the problematic cases illegal. Don't even think about 
> deepcopy vs array vs object etc., just let the const system 
> handle it.

I might be misinterpreting, but it seems like you're suggesting
```
S s;
s.arr[0] = "imm"; // compile-time error?
s.arr = ["new"];
s.arr[0] = "mut"; // ok
```
I'm not seeing how that would fly.

I can imagine it being easier done at runtime - with a bit of 
extra overhead - using mprotect or tagged pointers.