bool passed by ref, safe or not ?

[Quirin Schroll]

On Wednesday, 5 June 2024 at 18:31:12 UTC, Basile B. wrote:
> On Wednesday, 5 June 2024 at 01:18:06 UTC, Paul Backus wrote:
>> On Tuesday, 4 June 2024 at 16:58:50 UTC, Basile B. wrote:
>>> ```d
>>> 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
>>> }
>>> ```
>>>
>> [...]
>>>
>>> Do I corrupt memory here or not ?
>>> Is that a safety violation ?
>>
>> `cast(bool*)&a` is a safety violation.
>>
>> The only [safe values][1] for a `bool` are 0 (false) and 1 
>> (true). By creating a `bool*` that points to a different 
>> value, you have violated the language's safety invariants. 
>> Because of this, operations that would normally be safe 
>> (reading or writing through the `bool*`) may now result in 
>> undefined behavior.
>>
>> [1]: https://dlang.org/spec/function.html#safe-values
>
> Obviously the topic was created because of the recent move D 
> made. Sorry for the "catchy" aspect BTW. Now I remember that D 
> safety is unrelated to undefined behaviors.

I don’t think there’s any meaningful difference. If a program has 
UB, it can do anything, including corrupt memory. If a program 
corrupts memory, that’s UB. `@safe` means UB-free, which includes 
free of memory corruption.