On Wed, Oct 15, 2025 at 3:30 PM Timur Doumler <cpp_at_[hidden]> wrote:

>
>
> On 15 Oct 2025, at 15:20, Ran Regev <regev.ran_at_[hidden]> wrote:
>
>
>
> On Wed, Oct 15, 2025, 14:10 Timur Doumler via SG15 <sg15_at_[hidden]>
> wrote:
>
>> Specifically about the inconsistency that Tom highlighted:
>>
>> Please correct me if I'm wrong, but if I remember correctly, we discussed
>> this point specifically when reviewing the P3471 wording in CWG+LWG. From
>> what I remember, the outcome of that discussion was that we can (and did)
>> write in the wording that the standard library is using contract assertions
>> as defined in the core language (`pre`, `post`, and `contract_assert`) but
>> that does not actually imply that those keywords are physically present in
>> the standard library implementation, only that the standard library behaves
>> as if they were there.
>>
>> In other words, if a standard library implementation internally uses
>> macros — or some other implementation-defined mechanism — instead of the
>> contextual keywords `pre`, `post`, and `contract_assert`, then that
>> implementation is still conforming with that wording as long as the
>> observable behaviour is the same as if those keywords were used —
>>
> P2900 suggests that the contract semantics are selected by the one that is
> responsible for building the application, not the library writer.
> If the library uses a different tool that is not the contextual keywords,
> and thus allows different semantics for the library than for the
> application - is this within the "observable behaviour is the same as if
> those keywords were used"?
>
>
> Assuming that by "library", you mean "standard library":
>
> The mechanism for choosing the evaluation semantics of any particular
> evaluation of any assertion anywhere in the program is
> implementation-defined. It follows that allowing different
> contract-evaluation semantics for the standard library than for the rest of
> the program would be conforming. It follows further that offering one flag
> for choosing the contract-evaluation semantics of the standard library and
> a different flag for the contract-evaluation semantics of the rest of the
> program would be conforming too.
>
> Does that answer your question?
>
Yes, thanks.

>
> Timur
>
>