Andrew Pimlott andrew at pimlott.net
Mon Jan 24 11:50:44 EST 2005

On Mon, Jan 24, 2005 at 02:16:16PM +0100, Marcin 'Qrczak' Kowalczyk wrote:
> Keith Wansbrough <Keith.Wansbrough at cl.cam.ac.uk> writes:
> > In particular, people often want to compute with time differences:
> > next week, next month, next year, etc. These are calendar operations,
> > and defining precisely what they mean in edge cases is often tricky.
> > Even discounting leap seconds and the like, "next month" is sometimes
> > 28 days into the future, sometimes 29, sometimes 30, and sometimes
> > 31 - and sometimes makes little sense: when is "31 January 2005 plus
> > one month"?
> We should look how other languages solve that.

The best time library I've used is Perl's DateTime.  (Anyone who thinks
that everything in Perl is a bad hack, please suspend judgement for a
minute!)  It has DateTime, DateTime::Duration, and DateTime::TimeZone
classes (along with a host of supporting players, such as the handy
DateTime::Span), and addresses the various ambiguities.  (Another
example not yet discussed here:  The difference between two times can be
expressed in years, days, hours, or seconds, so the library lets you
choose.)  I believe it gets all the date math right, including leap
seconds.  It is the result of considerable development, use, and
experience with other time libraries.

The project is at


and if you click the modules link, you can read the documentation.  (As
I write, search.cpan.org seems to be dead, so you'll have to wait for
the documentation.  The FAQ might be useful in the mean time.)


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