I didn't say it was a good idea, I just said it's the status quo.

Cheers,
Timur

> On 20 Dec 2022, at 14:30, Lénárd Szolnoki via Std-Proposals <std-proposals_at_[hidden]> wrote:
>
> Hi,
>
>> On 20 December 2022 13:25:48 GMT, Timur Doumler via Std-Proposals <std-proposals_at_[hidden]> wrote:
>> 
>>
>>
>>>> On 19 Dec 2022, at 12:11, Bo Persson via Std-Proposals <std-proposals_at_[hidden]> wrote:
>>> At least originally, there was a basic idea that ignoring an attribute should not affect the validity of a program. Like [[nodiscard]] and [[maybe_unused]] would affect warnings, but not the generated code.
>>>
>>> Adding ABI-modifying attributes seems to be totally contrary to this.
>>
>> That basic idea has been thrown out of the window a while ago. We now have multiple potentially-ABI-modifying attributes in the standard.
>>
>> [[no_unique_address]] modifies ABI: its purpose is to literally change the class layout.
>>
>> [[assume]] can also modify ABI in one particular edge case (https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2022/p2552r1.pdf, see last code example on page 5).
>>
>> Cheers,
>> Timur
>
> Are the precedences confirm that it is a good idea though? [[no_unique_address]] had to be "backported" to earlier -std options in clang and gcc. The ABI mismatch exists between old and new versions of the compilers on older standards.
>
> MSVC just continues to ignore the attribute, AFAIK at least partly to avoid ABI issues.
>
> I think the ABI issues could have been side-stepped, if it was introduced by a non-ignorable syntax. Unfortunately there is no similarly convenient way to introduce those.
>
> I did not know about [[assume]].
>
> Cheers,
> Lénárd
> --
> Std-Proposals mailing list
> Std-Proposals_at_[hidden]
> https://lists.isocpp.org/mailman/listinfo.cgi/std-proposals