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Doing Date Arithmetic
CodeExpectedActual
require 'date'
y2k = Time.gm(2000, 1, 1)
 Sat Jan 01 00:00:00 UTC 2000 Sat Jan 01 00:00:00 UTC 2000 
y2k + 1
 Sat Jan 01 00:00:01 UTC 2000 Sat Jan 01 00:00:01 UTC 2000 
y2k - 1
 Fri Dec 31 23:59:59 UTC 1999 Fri Dec 31 23:59:59 UTC 1999 
y2k + (60 * 60 * 24 * 365)
 Sun Dec 31 00:00:00 UTC 2000 Sun Dec 31 00:00:00 UTC 2000 
y2k_dt = DateTime.new(2000, 1, 1)
(y2k_dt + 1).to_s
 "2000-01-02T00:00:00Z" "2000-01-02T00:00:00Z" 
(y2k_dt - 1).to_s
 "1999-12-31T00:00:00Z" "1999-12-31T00:00:00Z" 
(y2k_dt + 0.5).to_s
 "2000-01-01T12:00:00Z" "2000-01-01T12:00:00Z" 
(y2k_dt + 365).to_s
 "2000-12-31T00:00:00Z" "2000-12-31T00:00:00Z" 
day_one = Time.gm(1999, 12, 31)               
day_two = Time.gm(2000, 1, 1)
day_two - day_one
 86400.0 86400.0 
day_one - day_two
 -86400.0 -86400.0 
day_one = DateTime.new(1999, 12, 31)
day_two = DateTime.new(2000, 1, 1)
day_two - day_one
 Rational(1, 1) Rational(1, 1) 
day_one - day_two
 Rational(-1, 1) Rational(-1, 1) 
before_time = Time.now
before_datetime = DateTime.now
sleep(10)
Time.now - before_time
 10.003414 10.004279 
DateTime.now - before_datetime
 Rational(5001557, 43200000000) Rational(18527, 160000000) 
require 'rubygems'
require 'active_support'
10.days.ago
 Wed Mar 08 19:54:17 EST 2006 Tue Apr 04 17:32:20 EDT 2006 
1.month.from_now
 Mon Apr 17 20:54:17 EDT 2006 Sun May 14 17:32:20 EDT 2006 
2.weeks.since(Time.local(2006, 1, 1))
 Sun Jan 15 00:00:00 EST 2006 Sun Jan 15 00:00:00 EST 2006 
y2k - 1.day
 Fri Dec 31 00:00:00 UTC 1999 Fri Dec 31 00:00:00 UTC 1999 
y2k + 6.3.years
 Thu Apr 20 01:48:00 UTC 2006 Thu Apr 20 01:48:00 UTC 2006 
6.3.years.since y2k
 Thu Apr 20 01:48:00 UTC 2006 Thu Apr 20 01:48:00 UTC 2006 
(y2k_dt >> 1).to_s
 "2000-02-01T00:00:00Z" "2000-02-01T00:00:00Z" 
(y2k_dt << 1).to_s
 "1999-12-01T00:00:00Z" "1999-12-01T00:00:00Z" 
y2k + 1.month
 Mon Jan 31 00:00:00 UTC 2000 Mon Jan 31 00:00:00 UTC 2000 
y2k - 1.month
 Thu Dec 02 00:00:00 UTC 1999 Thu Dec 02 00:00:00 UTC 1999 
halloween = Date.new(2000, 10, 31)
(halloween << 1).to_s
 "2000-09-30" "2000-09-30" 
(halloween >> 1).to_s
 "2000-11-30" "2000-11-30" 
(halloween >> 2).to_s
 "2000-12-31" "2000-12-31" 
leap_year_day = Date.new(1996, 2, 29)
(leap_year_day << 1).to_s
 "1996-01-29" "1996-01-29" 
(leap_year_day >> 1).to_s
 "1996-03-29" "1996-03-29" 
(leap_year_day >> 12).to_s
 "1997-02-28" "1997-02-28" 
(leap_year_day << 12 * 4).to_s
 "1992-02-29" "1992-02-29"