--- self + other

    self  other ƤҤ֤ޤ
    other Ǥʤ other.to_ary ͤѤޤ
    ͤޤǤʤä㳰 TypeError ȯ
    ޤ

    :
        a = [1, 2]
        b = [8, 9]
        p a + b     #=> [1, 2, 8, 9]
        p a         #=> [1, 2]        (Ѳʤ)
        p b         #=> [8, 9]        (Ѳʤ)

