--- self << obj

    obj ɲäޤArray#push Ʊ̤Ǥ

      ary = [1]
      ary << 2
      p ary      # [1, 2]

    ޤΥ᥽åɤ self ֤ΤǡʲΤ褦Ϣ³
    񤯤ȤǤޤ

      ary = [1]
      ary << 2 << 3 << 4
      p ary   #=> [1, 2, 3, 4]

