From: "Ara.T.Howard" <ahoward@...>
Date: 2004-05-14T12:43:50+09:00
Subject: Re: Bug in Marshal?

On 13 May 2004, matt wrote:

> With the usual deep_copy:
> 
> # Deep copy
> class Object
>   def deep_copy
>     Marshal.load(Marshal.dump(self))
>   end
> end
> 
> I get the following (irb 0.9(02/07/03))
> 
> irb(main):001:0> fmt = "%m-%d-%Y %H:%M"
> => "%m-%d-%Y %H:%M"
> irb> original = Time.gm(2004, 04, 25, 22, 56)
> => Sun Apr 25 22:56:00 UTC 2004
> irb> copy = original.deep_copy
> => Sun Apr 25 18:56:00 Eastern Daylight Time 2004
> irb> [original, copy].map {|t| t.strftime(fmt)}
> => ["04-25-2004 22:56", "04-25-2004 18:56"]
> irb> original.hour
> => 22
> irb> copy.hour
> => 18
> irb> original.hour <=> copy.hour
> => 1
> irb> original <=> copy
> => 0
> 
> Ruh Roh!

i think this actually makes sense if you consider that a Time object is only
storing the seconds since 1970 and the environment (TZ) affect how it's
interpreted:

  ~ > TZ=America/Boston ruby -e 'p Time.now'
  Fri May 14 03:25:38 America/Boston 2004

  ~ > TZ=America/Denver ruby -e 'p Time.now'
  Thu May 13 21:25:44 MDT 2004

consider that you might Marshal a Time object into some file, and that file
gets shipped to africa - you definitely want some sort of 'absolute' time in
there.  however, there's no problem if, when the file is loaded back in, the
Time object respects the locale settings - under the hood the time is still
the same:

  irb(main):001:0> original = Time.gm(2004, 04, 25, 22, 56)
  => Sun Apr 25 22:56:00 UTC 2004

  irb(main):002:0> copy = Marshal.load(Marshal.dump(original))
  => Sun Apr 25 16:56:00 MDT 2004

  irb(main):003:0> original.to_f
  => 1082933760.0

  irb(main):004:0> copy.to_f
  => 1082933760.0


if we compare hours we are comparing ints, if we compare seconds since 1970 in
either int or float we get and accurate comparison - which Time#<=> shows with
the 0 result.

-a
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