From: Ralph Shnelvar <ralphs@...32.com>
Date: 2009-11-14T21:20:00+09:00
Subject: Re: how to copy array in ruby

l> Array#dup creates a copy of the array, not of the elements in the
l> array, aka a shallow copy.

Is there a way to make a deep copy?  That is ... in the code below,
could b.dup be replaced with something like b.deepdup?


irb(main):019:0> a1 = [1,2,3,4]
=> [1, 2, 3, 4]
irb(main):020:0> b = [a1,5]
=> [[1, 2, 3, 4], 5]
irb(main):021:0> c1 = b
=> [[1, 2, 3, 4], 5]
irb(main):022:0> c2 = b.dup
=> [[1, 2, 3, 4], 5]
irb(main):023:0> a1[0] = "hi"
=> "hi"
irb(main):024:0> a1
=> ["hi", 2, 3, 4]
irb(main):025:0> c1
=> [["hi", 2, 3, 4], 5]
irb(main):026:0> c2
# because of the shallow copy, c2[0][0] is "hi" instead of a naively
# assumed 1.
=> [["hi", 2, 3, 4], 5]
irb(main):027:0> c1[1] = "bye"
=> "bye"
irb(main):028:0> c1
=> [["hi", 2, 3, 4], "bye"]
irb(main):029:0> c2
# The shallow copy gives the expected result for c2[1], below.
=> [["hi", 2, 3, 4], 5]