From: Michael Neumann <neumann@...>
Date: 2001-11-19T06:22:58+09:00
Subject: [ruby-talk:25789] Re: Array.new(n, Array.new(m)) weirdness, but "select isn't broken"

Chris Reay wrote:
> The following occurs ...
> 
> irb(main):001:0> a = Array.new(3, Array.new(3))
> [[nil, nil, nil], [nil, nil, nil], [nil, nil, nil]]
> irb(main):002:0> a[1][1] = 0
> 0
> irb(main):003:0> a
> [[nil, 0, nil], [nil, 0, nil], [nil, 0, nil]]
> 
> .... however I would have expected (and hoped for) ...
> [[nil, nil, nil], [nil, 0, nil], [nil, nil, nil]]

p a[0].id
p a[1].id
p a[2].id

return all the same id. This is because 

  a = Array.new(3, Array.new(3))

is the same as

  b = Array.new(3)
  a = Array.new(3, b)

which creates an array with three references to "b"

Maybe further versions of Ruby will have a block form like that

  a = Array.new(3) { Array.new(3) }

In this case the block gets evaluated three times and would create three
different objects.


Regards,

  Michael 

-- 
Michael Neumann
merlin.zwo InfoDesign GmbH
http://www.merlin-zwo.de