--- index(pattern[, pos])

    ʬʸõü鱦ü˸äƹԤޤĤäʬʸ
    κüΰ֤֤ޤĤʤ nil ֤ޤ

     pattern ˤõʬʸλʸʸ
    ɤ򼨤 0  255 ɽΤ줫ǻꤷޤ

    pos Ϳ줿ˤϤΰ֤õޤpos ξ
    άͤ 0 Ǥ

        p "astrochemistry".index("str")         # => 1
        p "character".index(?c)                 # => 0
        p "regexpindex".index(/e.*x/, 2)        # => 3

    pos ξ硢ʸ֤õޤ

        p "foobarfoobar".index("bar", 6)        # => 9
        p "foobarfoobar".index("bar", -6)       # => 9

    rindex ⻲ȤƤ

