From: Johan Veenstra <johan.veenstra@...>
Date: 2007-02-09T06:17:38+09:00
Subject: Re: Calculating a future date

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On 2/6/07, Alexandru E. Ungur <alexandru@globalterrasoft.ro> wrote:
>
> >>> sender: "Toine" date: "Tue, Feb 06, 2007 at 08:00:06PM +0900" <<<EOQ
> > Date.today + 31 and Time.now + 31*24*60*60 yield the same results.
> Just beware that although they yield the same result they do it at
> *very* different speeds:
>
> ~>> cat date_vs_time.rb
> require 'benchmark'
> require 'date'
>
> n = 100_000
> Benchmark.bm do |x|
>   x.report { n.times do a = Date.today+31; end }
>   x.report { n.times do a = Time.now+2678400; end }
> end
>
>
> ~>> ruby date_vs_time.rb
>       user     system      total        real
> 24.300000   0.760000  25.060000 ( 31.808122)
>   0.410000   0.440000   0.850000 (  0.971718)
>
>
> So, whenever you can get away with Time, use it. Only use Date when
> you have to.
>
>
> Cheers,
> Alex
>
>

require 'date'

puts Date.today
puts Date.today + 100
puts Time.now
puts Time.now + 100*24*60*60

2007-02-08
2007-05-19
Thu Feb 08 22:05:49 W. Europe Standard Time 2007
Sat May 19 23:05:49 W. Europe Daylight Time 2007

Looks innocent enough, but when I run the same program again in 60 minutes,
Time.now + 100*60*60 would output:
Sun May 20 00:05:49 W. Europe Daylight Time 2007 (which is my birthday by
the way).

So from a correctness point of view, use Date when you are dealing with
dates,
and use Time when you are dealing with time.

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