Section: 29.5.10 [time.duration.alg] Status: NAD Submitter: Charlie Barto Opened: 2022-07-16 Last modified: 2022-11-30 17:59:24 UTC
Priority: Not Prioritized
View all issues with NAD status.
Currently 29.5.10 [time.duration.alg] specifies abs(duration) as:
Returns: if d >= d.zero(), return d, otherwise return -d.
Because unary minus on durations is defined to return common_type_t<duration>(-rep_), and common_type_t for durations is specified to reduce the period, this is ill-formed with durations such as duration<int, ratio<1000, 1000>>, or any other type where the numerator and denominator of the period are not coprime.
[2022-08-23; Reflector poll: NAD]
Not ill-formed, implementation should do a conversion. Changing it to return the reduced duration as an improvement would be for LEWG.
[2022-11-30 LWG telecon. Status changed: Tentatively NAD → NAD.]
This wording is relative to N4910.
Modify 29.2 [time.syn], header <chrono> synopsis, as indicated:
[…] // 29.5.10 [time.duration.alg], specialized algorithms template<class Rep, class Period> constexpr duration<Rep, Period> abs(duration<Rep, Period> d); […]
Modify 29.5.10 [time.duration.alg] as indicated:
[Drafting note: This will cause abs to reduce the period before returning it, much like the other arithmetic operators.This is not a breaking change, because code that was using abs with a non-reduced period before did not compile. ]
template<class Rep, class Period> constexpr duration<Rep, Period> abs(duration<Rep, Period> d);
-1- Constraints: numeric_limits<Rep>::is_signed is true.-2- Returns: If d >= d.zero(), return d, otherwise return -d.