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Section: 29.11.7.2 [time.zone.zonedtime.ctor] Status: C++20 Submitter: Tomasz Kamiński Opened: 2019-06-23 Last modified: 2021-02-25
Priority: 2
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Discussion:
zoned_time constructors with string_view and
another zoned_time are not accepting zoned_time
instances that use a different time zone representation (TimeZonePtr parameter):
zoned_time(string_view name, const zoned_time<Duration>& zt); zoned_time(string_view name, const zoned_time<Duration>& zt, choose);
This makes them inconsistent with the constructors from TimeZonePtr
and zoned_time, that they delegate to:
template<class Duration2, class TimeZonePtr2> zoned_time(TimeZonePtr z, const zoned_time<Duration2, TimeZonePtr2>& zt); template<class Duration2, class TimeZonePtr2> zoned_time(TimeZonePtr z, const zoned_time<Duration2, TimeZonePtr2>& zt, choose);
Furthermore it forces the creation of a temporary zoned_time object in
case when the source uses the same TimeZonePtr, but different Duration.
This wording is relative to N4820.
Modify 29.11.7.1 [time.zone.zonedtime.overview], class template zoned_time synopsis, as indicated:
template<class Duration2, class TimeZonePtr2> zoned_time(string_view name, const zoned_time<Duration2, TimeZonePtr2>& zt); template<class Duration2, class TimeZonePtr2> zoned_time(string_view name, const zoned_time<Duration2, TimeZonePtr2>& zt, choose);Modify 29.11.7.2 [time.zone.zonedtime.ctor] as indicated:
template<class Duration2, class TimeZonePtr2> zoned_time(string_view name, const zoned_time<Duration2, TimeZonePtr2>& y);-32- Remarks: This constructor does not participate in overload resolution unless zoned_time is constructible from the return type of traits::locate_zone(name) and zoned_time<Duration2, TimeZonePtr2>.
-33- Effects: Equivalent to construction with {traits::locate_zone(name), y}.template<class Duration2, class TimeZonePtr2> zoned_time(string_view name, const zoned_time<Duration2, TimeZonePtr2>& y, choose c););-34- Remarks: This constructor does not participate in overload resolution unless zoned_time is constructible from the return type of traits::locate_zone(name), zoned_time<Duration2, TimeZonePtr2>, and choose.
-35- Effects: Equivalent to construction with {traits::locate_zone(name), y, c}. -36- [Note: The choose parameter has no effect. — end note]
[2020-02-13, Prague]
During LWG discussions it was suggested to rebase the wording to reduce the chances for confusion.
[2020-02 Status to Immediate on Thursday morning in Prague.]
Proposed resolution:
This wording is relative to N4849.
Modify 29.11.7.1 [time.zone.zonedtime.overview], class template zoned_time synopsis, as indicated:
template<class Duration2, class TimeZonePtr2> zoned_time(string_view name, const zoned_time<Duration2, TimeZonePtr2>& zt); template<class Duration2, class TimeZonePtr2> zoned_time(string_view name, const zoned_time<Duration2, TimeZonePtr2>& zt, choose);
Modify 29.11.7.2 [time.zone.zonedtime.ctor] as indicated:
template<class Duration2, class TimeZonePtr2> zoned_time(string_view name, const zoned_time<Duration2, TimeZonePtr2>& y);-32- Constraints: zoned_time is constructible from the return type of traits::locate_zone(name) and zoned_time<Duration2, TimeZonePtr2>.
-33- Effects: Equivalent to construction with {traits::locate_zone(name), y}.template<class Duration2, class TimeZonePtr2> zoned_time(string_view name, const zoned_time<Duration2, TimeZonePtr2>& y, choose c););-34- Constraints: zoned_time is constructible from the return type of traits::locate_zone(name), zoned_time<Duration2, TimeZonePtr2>, and choose.
-35- Effects: Equivalent to construction with {traits::locate_zone(name), y, c}. -36- [Note: The choose parameter has no effect. — end note]