Ruby1.8.7で前日のTimeオブジェクトを取得する

time.rb

# ruby 1.8.7 only
# 前日のTimeオブジェクトを取得する

## パターン１：Timeクラスに Time#prev_day を追加
class Time

  def next_day( n = 1, reset = true )
    time = self + 60 * 60 * 24 * n
    _hour, _min, _sec = reset ? [ 0, 0, 0 ] : [ hour, min, sec ]
    Time.local( time.year, time.month, time.day, _hour, _min, _sec )
  end

  def prev_day( n = 1, reset = true )
    time = self - 60 * 60 * 24 * n
    _hour, _min, _sec = reset ? [ 0, 0, 0 ] : [ hour, min, sec ]
    Time.local( time.year, time.month, time.day, _hour, _min, _sec )
  end

end

p Time.now.prev_day

## パターン２：Dateオブジェクトに特異メソッド .to_time を追加
require "date"

yesterday = Date.today - 1
def yesterday.to_time
  Time.local( year, mon, day )
end

p yesterday.to_time

## パターン３：Timeクラスから作成
yesterday = Time.now - 60 * 60 * 24 * 1
p Time.local( yesterday.year, yesterday.mon, yesterday.day )

## パターン４：Dateクラスから作成
require "date"

yesterday = Date.today - 1
p Time.local( yesterday.year, yesterday.mon, yesterday.day )