Re: Seconds left in day + DST

On Thu, 19 Jun 2008, Jim Spath wrote:

> I'm a bit unclear on how to properly deal with DST when determining the 
> number of seconds left in a day.
>
> Here's what I have now:
>
> my $now = DateTime->now(time_zone => 'local');
>
> my $tom =
>  ($dt + DateTime::Duration->new(days => 1))->truncate(to => 'day'));
>
> my $seconds_left = $tom_dt->epoch() - $dt->epoch();
>
> It seems to work fine, but another developer here mentioned that it might not 
> handle DST properly, although he wasn't sure how to do it himself.

There is a method to do subtraction between two datetimes and return the 
difference in seconds, subtract_datetime_absolute(). It handles leap 
seconds and DST properly.

Your method will also work for DST, but it's a little clunky, plus it 
won't work outside the limited range of the epoch.

Generally speaking, you should only use the epoch when you have to 
interact with some non-DateTime module/system that requires epochs. 
Otherwise stick with the DateTime.pm-provided methods for maximum 
correctness and flexibility (and slowness, unfortunately ;)


-dave

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