--- join([sep])

    Ǥʸ sep ֤˶Ϣ뤷ʸ֤ޤ
    ʸǤʤǤФƤ to_s ̤Ϣ뤷ޤ
    ǤǤкƵŪ(Ʊ sep Ѥ) join 
    ʸϢ뤷ޤ

    sep ά줿ˤѿ $, ͤȤޤ

    : ǤȤޤ褦̵¤˥ͥȤФƤϡʲ
    Τ褦ʷ̤ˤʤޤ

        ary = [1,2,3]
        ary.push ary
        p ary           # => [1, 2, 3, [...]]
        p ary.join      # => "123123[...]"

