$ irb
irb(main):001:0> $x = [ 1, 2, 3 ]
=> [1, 2, 3]
irb(main):002:0> $y = [ $x, 4, 5, 6 ]
=> [[1, 2, 3], 4, 5, 6]
irb(main):003:0> $x.object_id
=> 270640
irb(main):005:0> $y[0].object_id
=> 270640
irb(main):006:0> ^D
$ irb
irb(main):001:0> $x
=> [1, 2, 3]
irb(main):002:0> $y
=> [[1, 2, 3], 4, 5, 6]
irb(main):003:0> $x.object_id
=> 40280
irb(main):004:0> $y[0].object_id
=> 40280

うまくいったぽ??