From: Michael McDaniel <ruby@...>
Date: 2002-04-01T17:09:34+09:00
Subject: Re: Timezone name -> UTC hour offset?

Sean Chittenden wrote:

>> > Is there any way of going from -0800 to (PST|PDT) ?  Is there a
>> > module that does this?  -sc
>>
>> The simple case of adding 8 hours to time is (assuming you wanted to
>> check that time was utc, and you want to convert to PST)
>>
>> if time.gmt?
>>   t2 = time + 28800
>> end
>>
>> (8 hours * 60 minutes * 60 seconds = 28800)
> 
> Thanks for the idea!  It ain't pretty, but this works pretty well for
> converting timezones (ex: "-0800", "-0730", etc...).
^^^^^^^^^^^^^^^^
you are welcome

> 
> @date = @date + (("-0730".to_i.abs.divmod(100)[0] * 3600) +
>                  ("-0730".to_i.abs.divmod(100)[1] * 60))
> 
> Is there any way to increment a time object without creating a new
> object?  Something like a +! or t.add_s!(sec) operator?  -sc
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 
Nothing that I was able to find.  From the Nutshell book (or goat book, as 
I've seen Matz write), I paraphrase slightly...

t is a Time object 

t + n 
returns a Time object with n number of seconds added.
  
t - x
If x is another Time object, returns time difference in seconds as Float 
object.  If x is a number, returns a Time object with number of seconds 
subtracted.

I found nothing about modifying an object in place by adding/subtracting 
seconds.

I couldn't figure out how to convert seconds back to a Time object (e.g. 
t.to_f returns seconds as Float since the epoch (or t.to_i for Integer), 
but no way I know to convert that Float (or Integer) value back to a Time 
object or date string (e.g. in Tcl 'clock format [clock seconds]' returns 
the present date ('clock seconds' returns #seconds since the epoch)).

Maybe an add_s!(sec) operator would be a useful enhancement for the future. 
 Probably easy to add, since a time object internally is "...stored as a 
number of seconds since the epoch...".  Then again, maybe there is a 
specific reason why a Time object, which corresponds to a certain time, was 
designed to be, in effect, immutable.

(epoch == 00:00:00 January 1 1970, the (folklorish?) date of the birth of 
UNIX(tm))

~mm