[ruby-talk:13292] Re: Time Travel with Ruby

At 06:10 3/29/2001 +0900, you wrote:
>On Thu, 29 Mar 2001 03:55:31 +0900, Ernest Ellingson pontificated:
>+ Well you can blame it on Windows but has anyone tried this on other systems.
>+ t=Time.local(2001, 4,1,2,0)
>+ puts t
>
>% uname -a && ruby -e 'p Time.local(2001, 4, 1, 2, 0)' && ruby -v
>Linux vilya 2.4.2 #6 Fri Mar 16 14:12:57 EST 2001 i686 unknown
>Sun Apr 01 03:00:00 EDT 2001
>ruby 1.6.2 (2001-01-18) [i686-linux]
>
>% uname -a && ruby -e 'p Time.local(2001, 4, 1, 2, 0)' && ruby -v
>OpenBSD narya 2.7 GENERIC#25 i386
>Sun Apr 01 03:00:00 EDT 2001
>ruby 1.6.2 (2001-01-18) [i386-openbsd2.7]
>
>% uname -a && ruby -e 'p Time.local(2001, 4, 1, 2, 0)' && ruby -v
>SunOS laplace.stat.cwru.edu 5.7 Generic_106541-12 sun4u sparc
>Sun Apr 01 01:00:00 EST 2001
>ruby 1.6.3 (2001-02-24) [sparc-solaris2.7]
>
>% uname -a && ruby -e 'p Time.local(2001, 4, 1, 2, 0)' && ruby -v
>AIX theory2 2 4 000069614600 unknown
>Sun Apr 01 01:00:00 EST 2001
>ruby 1.6.2 (2001-01-18) [powerpc-aix4.2.0.0.0]
>
>--
>ruby -F- -e '$, = $; . sub /./, " Another "; print %w.Just Rewbie .. join'
Thanks for all the feedback.  I'm using Ruby 1.6.2 and I see you are using 
it also.  Looks like Sun and Microsoft can't tell time very well.  I'm not 
sure how local time is being calculated but I'm guessing that the 
fundamental problem is that Sun and Microsoft are reporting daylight 
savings time not being in effect at 02:00 on April 1 and Linux and BSD are 
reporting it IS in effect.
The only way I can think to calculate the time is to start with UTC and 
apply a time zone offset that is determined by DST being on or off.  We 
could debate forever whether DST is on or off at 02:00.  By definition, DST 
does not have an 02:00 hour on April 1, 2001.  I'm not sure Ruby returns 
the correct hour on any of the systems.  It should be returning 'time 
doesn't exist'.  In two cases, Sun and MS, Ruby moves the hour back in 
order to return a Time.  On Linux and BSD it moves the hour ahead to return 
a time.  My guess is that the same algorithm is used on all the systems and 
that there is only a variation on isdst.  Sun and MS return false and Linux 
and BSD return true.

The inventors of DST only hoped to get the whole world to start work an 
hour early during the days with long daylight hours.  I'm sure they weren't 
aware of all the un intended consequences.

Ernie