Dear experts,
a few days ago I have got great help from this list, so I hope I may ask
another (probably stupid) question (I am now having the opposite problem
than back then):
Using DateTime, is it possible to tell in advance if a certain date-time
which is given in a certain locale will be ambiguous due to switching
from DST to standard time?
Example (taken from DateTime's documentation):
my $dt = DateTime->new(
year => 2003,
month => 10,
day => 26,
hour => 1,
minute => 30,
second => 0,
time_zone => 'America/Chicago',
);
Now $dt is ambiguous: The clock has been turned back to 01:00:00 h at
02:00:00 that night, so the time 01:30:00 h has occurred twice.
Even after thinking many hours about it, I haven't found a reasonable
general method to determine if an arbitrary date-time is ambiguous in
the sense above.
Possibly, I could subtract different time spans from the date-time in
question and check if the result is the expected one and use that to
find out if it is ambiguous, but this would cost much CPU time.
So I would like to ask if somebody knows a general, reasonable method
for solving that problem, given the following conditions:
1) We don't know the time span the clock is turned back when switching
from DST to standard time. It might be one hour in most time zones /
countries, but after all, some weird person could decide that it is 18
minutes and 13 seconds or 5 hours, 53 minutes and 42 seconds.
2) We don't know whether the point in time when the switch occurs is
exactly at an hour's end / begin. Again, some weird person could decide
that the switch happens at 08:48:27 am.
I know that there are not many persons on the world that are *that*
weird, but on the other hand, I don't want to implement an algorithm
which uses assumptions which are not safe.
As a last resort, there is at least one other module (AFAIK) which I
could use to extract the daylight saving switching times and time spans
from the time zone database, and I could use that information to solve
my problem. But this would probably mean to reinvent the wheel, so I'd
like to avoid it.
Thank you very much in advance,
Binarus
