On 7 March 2025 01:14:17 GMT, Jeremy Rifkin via Std-Proposals <std-proposals_at_[hidden]> wrote:
>>> In looking, it seems to me that making
>>> std::chrono::system_clockusable in
>>> constexpr contexts is pretty simple and invokes marking one function as
>>> constexpr: now.
>>
>> Please don't.
>
>+1

+1

This is an ODR footgun among other concerns about reproducible builds. The following is instant ODR violation, if appears in multiple TUs and the clock is not faked:

inline constexpr auto x = std::chrono::system_clock::now();

>
>Also this strikes me as a good way to violate ODR.
>
>Cheers,
>Jeremy
>
>On Mar 6 2025, at 4:00 pm, Thiago Macieira via Std-Proposals
><std-proposals_at_[hidden]> wrote:
>
>> On Thursday, 6 March 2025 13:43:47 Pacific Standard Time Nikolaos D.
>> Bougalis
>> via Std-Proposals wrote:
>>> In looking, it seems to me that making
>>> std::chrono::system_clockusable in
>>> constexpr contexts is pretty simple and invokes marking one function as
>>> constexpr: now.
>>
>> Please don't. Your software should not depend on the time it was
>> compiled at
>> and should not change depending on that.
>>
>> std::chrono::system_clock::time_point now = {};
>> if (!std::is_constant_evaluated()))
>> now = std::chrono::system_clock::now();
>>
>>> Less exotic use cases include the ability to generate time-based
>>> UUIDs at
>>> compile time, to seed random number generators at compile time, potentially
>>> warn when old code is compiled (not that there's anything wrong with that!)
>>
>> Please make your software reproducible: it should be bitwise exactly
>> identical
>> if it is compiled by the same compiler.
>>
>> --
>> Thiago Macieira - thiago (AT) macieira.info - thiago (AT) kde.org
>> Principal Engineer - Intel DCAI Platform & System Engineering
>>
>>
>>
>> --
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>>