bool passed by ref, safe or not ?

[rkompass]

On Tuesday, 4 June 2024 at 16:58:50 UTC, Basile B. wrote:
> question in the header, code in the body, execute on a X86 or 
> X86_64 CPU
>
> ```d
> module test;
>
> void setIt(ref bool b) @safe
> {
>     b = false;
> }
>
> void main(string[] args)
> {
>     ushort a = 0b1111111111111111;
>     bool* b = cast(bool*)&a;
>     setIt(*b);
>     assert(a == 0b1111111100000000); // what actually happens
>     assert(a == 0b1111111111111110); // what would be safe
> }
> ```
>
> I understand that the notion of `bool` doesn't exist on X86, 
> hence what will be used is rather an instruction that write on 
> the lower 8 bits, but with a 7 bits corruption.
>
> Do I corrupt memory here or not ?
> Is that a safety violation ?

No everything is fine.
The bool is the same size like byte or char.
So your cast makes &a pointer to a byte.
And this byte has to be made completely zero by setIt, otherwise 
it would not be false in the sense of bool type.