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weekday_indexed
to range of [0, 7]
Section: 29.8.7.2 [time.cal.wdidx.members] Status: C++20 Submitter: Howard Hinnant Opened: 2019-09-02 Last modified: 2021-02-25
Priority: 0
View all issues with C++20 status.
Discussion:
On one hand, we say that if you try to construct a weekday_indexed
with index 0,
you get an unspecified index instead (29.8.7.2 [time.cal.wdidx.members]/p1),:
The values held are unspecified if
!wd.ok()
or index is not in the range[1, 5]
.
OTOH, we take pains to pin down year_month_weekday
's conversion to sys_days
when the index is zero (29.8.7.2 [time.cal.wdidx.members]/p19):
If
index()
is0
the returnedsys_days
represents the date7
days prior to the firstweekday()
ofyear()/month()
.
This is inconsistent. We should allow a slightly wider range (say, [0, 7]
, since you need
at least 3 bits anyway to represent the 5 distinct valid values, and the 0
value referred
to by 29.8.7.2 [time.cal.wdidx.members]/p19.
[2019-09-24 Issue Prioritization]
Status to Tentatively Ready and priority to 0 after six positive votes on the reflector.
Proposed resolution:
This wording is relative to N4830.
Modify 29.8.7.2 [time.cal.wdidx.members] as indicated:
[Drafting note: As a drive-by fix a cleanup of "Constructs an object of type
weekday_indexed
" wording has been applied as well. ]
constexpr weekday_indexed(const chrono::weekday& wd, unsigned index) noexcept;-1- Effects:
Constructs an object of typeInitializesweekday_indexed
by initializingwd_
withwd
andindex_
withindex
. The values held are unspecified if!wd.ok()
orindex
is not in the range[
.10,57]