In message "[ruby-list:15284] Re: 年月を範囲でうまく扱うには？"
    on 99/07/07, Yukihiko Eda <yuki-e / geocities.co.jp> writes:
>> 大した手間でもなさそうだし、年月のクラスを作っちゃうのは
>> どうでしょうか??
>
>ありがとうございます。さっそく試してみます。

10分くらいで書いたのでバグバグでした。
少しまともにしたのを送ります。

Month

Included modules
  Comparable

Class methods

  new(y,m)
    creates new month oject for year y, month m

Methods

  year
  month
    returns a integer

  succ
    returns its next month

  <=>, <=, =>, <, >, ==
    comparison methods between months

  has?(date_or_time)
    returns if Date or Time is in the month or not.

  inspects
  to_s
    returns a human readable string

require "date"

class Month
  include Comparable

  Monthtag = [
    "January","February","March","April", "May", "June","July",
    "August", "September", "October", "November", "December"
  ]

  def initialize(y, m)
    unless y.kind_of?(Integer) && m.kind_of?(Integer) && 1..12 == m
      raise ArgumentError.new
    end

    @t = y*12 + m - 1
  end

  def year
    @t/12
  end

  def month
    @t%12 + 1
  end

  def succ(n = 1)
    t = @t + n
    Month.new(t/12, t%12 + 1)
  end

  def <=>(o)
    if o.kind_of?(Month)
      @t <=> o.year*12 + o.month - 1
    end
  end

  def has?(o)
    if o.kind_of?(Date) or o.kind_of?(Time)
      @t == o.year*12 + o.month - 1
    end
  end

  def inspect
    format("%04d-%02d", @t/12, @t%12 + 1)
  end

  def to_s
    Monthtag[@t%12][0..2] + " #{@t/12}"
  end
end

if __FILE__ == $0
  mrange = Month.new(1997,1)..Month.new(1999,12)
  today = Date.new(Time.now.year, Time.now.month)
  now = Time.now
  
  $\ = "\n"; $, = ", "

  for i in mrange
    print i, i.has?(today), i.has?(now)
  end
end