--- length
--- size

    ϰϤĹ֤ޤ
    Ƚü Integer Υ󥹥󥹤ʤ
        (last - first + (exclude_end? ? 0 : 1))
    ǤʳǤϡeach ¹ԤϰϤĹޤ

    ruby 1.7 feature: length, size ᥽åɤϤʤʤޤ
    ɬפʤ
      p ("a" .. "z").to_a.size
      => 26
    ʤɤȤɬפޤ

