[Development] Two-digit dates: what century should we use ?
edward.welbourne at qt.io
Thu Nov 7 11:47:20 CET 2019
André Somers (6 November 2019 17:20) wrote
> I came to the conclusion that the sane behavior for interpreting dates
> depends on the semantics of what the date means. For instance, a birth
> date will always be a date in the past,
... except when it's the best-estimate date of birth of an expected
child, or part of a discussion of how (say) an education system will
handle the cohorts of children born in various date ranges. I'll agree,
though, that birth dates are *usually* in the past ;^>
Even when it is in the past, the range of past dates it may land in is
more than a century wide. Some folk live for more than a century; and
records of dates of birth of folk can be relevant even after the folk in
question are dead.
(All of which argues against using two-digit years in dates of birth,
common though that practice is.)
> while a date for an appointment would normally be a date in the
and usually not very far in the future, at that, which makes this one
of the cases where two-digit years aren't automatically a bad idea.
> That alters the interpretation of the date. May I suggest adding an
> enum argument to any function doing the conversion from a string to a
> date that allows you tell you to suggest the kind of date that is
That would imply inventing (and documenting) how we're going to
implement each member of the enum; and, fundamentally, that's going to
boil down to specifying (per enum member) a range of (up to) 100 years
that each two-digit year value gets mapped into. Then along comes some
user whose use-case we didn't think of and we need to extend the enum
and the enum grows endlessly. I think it is easier to let the caller
just specify that year range (principally by its start date). The
caller can then invent any flavour of year range they like.
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