--- self =~ other

    ɽ other ȤΥޥåԤޤޥåХޥ
    ֤Υǥå򡢤Ǥʤ nil ֤ޤ
    other ʸǤäˤϤɽ˥ѥ뤷 
    self ФޥåԤޤ

    ξȤ߹ѿ $~ ˥ޥå˴ؤ
    ꤵޤ

    ruby 1.7 feature:
    other ʸǤäˤ self.index(other) Ԥޤ
    ξϡ$~ ѲϤޤ

    other ɽǤʸǤʤ
        other =~ self
    Ԥޤ

