From: ara.t.howard@...
Date: 2006-01-18T06:27:17+09:00
Subject: Re: Time Diff Module

On Wed, 18 Jan 2006, David Clements wrote:

> Anyone know of a module out there that will encapsulate differences in time?
>
> Ideally I would want something like this:
>
> d1 = DateTime.now + 2.hours + 2.minutes
> d2 = DateTime.now
>
> diff = d1-d2
>
>
> puts "Diff:  #{diff.hours}:#{diff.minutes}"
>
>
>>> Diff: 2:02
>
> I have searched for examples and all of them seem to be doing this manually.

i'm guessing the reason this has not been done generically is that it is
incredibly slippery.  for instance, if i had

   a = DateTime::new 1582, 8, 4
   b = a + 1.day

then b should the the day '1582-08-15'.  and

   diff = b - a
   p diff.days

should output either 10 or 1 - depending on how you look at it.

the reason is the fact that DateTime makes all the calender reforms between
julian and gregorian transparent and even handles them based on timezone.  not
saying it could not be done, but it's tough and, afaik, hasn't been.  see
ruby-1.8.4/lib/date.rb for details.

of course, activesupport give you Numeric#days, etc, but that is quite easy to
roll.

if the code you posted is pretty close you what you actually need then why not
simply use Time objects, converting to DateTime as needed using
DateTime::new(t.year, t.month, t.day... etc)?

     harp:~ > cat a.rb
     class Time
       module Units
         def __less__() "/" end
         def __more__() "*" end
         def milliseconds() self.send(__less__,1000) end; alias_method "millisecond", "milliseconds"
         def seconds() self end; alias_method "second", "seconds"
         def minutes() seconds.send(__more__,60) end; alias_method "minute", "minutes"
         def hours() minutes.send(__more__,60) end; alias_method "hour", "hours"
         def days() hours.send(__more__,24) end; alias_method "day", "days"
         def weeks() days.send(__more__,7) end; alias_method "week", "weeks"
         def months() weeks.send(__more__,4) end; alias_method "month", "months"
         def years() months.send(__more__,12) end; alias_method "year", "years"
         def decades() years.send(__more__,10) end; alias_method "decade", "decades"
         def centuries() decades.send(__more__,10) end; alias_method "century", "centuries"
       end
       module DiffUnits
         include ::Time::Units
         def __less__() "*" end
         def __more__() "/" end
       end
       alias_method "__delta__", "-"
       def - other
         ret = __delta__ other
         ret.extend DiffUnits
         ret
       end
     end
     class Numeric
       include ::Time::Units
     end

     now = Time::now
     a = now
     b = now + 2.hours + 2.minutes
     d = b - a

     require "yaml"
     %w( seconds minutes hours days ).each{|m| y m => d.send(m)}


     harp:~ > ruby a.rb
     ---
     seconds: 7320.0
     ---
     minutes: 122.0
     ---
     hours: 2.03333333333333
     ---
     days: 0.0847222222222222


hmmm.  maybe i'll add this to alib...

cheers.

-a
-- 
strong and healthy, who thinks of sickness until it strikes like lightning?
preoccupied with the world, who thinks of death, until it arrives like
thunder?  -- milarepa