: self - x
  x ե֥Ȥʤ顢դĤκ֤ޤ
  뤤
  x ͤʤСself  x դ֤ޤ
  
  1.8.0 ʹߤ Rational ֤ޤ ruby 1.8 feature

    $ ruby -v -rdate -e 'p(Date.new(2003,6,24) - Date.new(2003,6,23))'
    ruby 1.6.7 (2002-03-01) [i386-openbsd3.1]
    1

    $ ruby -v -rdate -e 'p(Date.new(2003,6,24) - Date.new(2003,6,23))'
    ruby 1.8.0 (2003-03-24) [i686-linux-gnu]
    Rational(1, 1)

