Forum: Ruby ruby dup unexpected behaviour

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983428278161aebf0513417242794952?d=identicon&s=25 David Maciejak (Guest)
on 2009-06-09 11:52
(Received via mailing list)
Hi,

I got no answer on ubuntu entry at
https://bugs.launchpad.net/ubuntu/+source/ruby1.8/...
so I resend it here. Does someone have any clues on this ?

Thanks,
david


--------------------------------------------------------------------------------------

Hi,

got some strange result in ruby1.8 (1.8.7.72-3) on jaunty (up to date).
Don't know if I use correctly dup function but my duped hash is
modified even if i call the freeze method. Below the quick and dirty
test case showing that @c member of the class Global is modified


#!/usr/bin/ruby

class Testme
 attr_accessor :value
 def initialize(val)
  @value=val
 end
 def Testme::bou(val)
  $a["b"].value=val
 end
 def to_str()
  print @value,"\n"
 end
end

class Global

 def initialize
  @c=nil
 end

 def go()
  @c=$a.dup
  @c.freeze
  #print value before the changes
  to_str()
 end
 def to_str()
  print @c,"\n"
 end

end

$a=Hash.new
$a["a"]=Testme.new(1)
$a["b"]=Testme.new(2)

main=Global.new
main.go()
Testme::bou(3)
#print value after the changes
main.to_str()
753dcb78b3a3651127665da4bed3c782?d=identicon&s=25 Brian Candler (candlerb)
on 2009-06-09 12:19
David Maciejak wrote:
> I got no answer on ubuntu entry at
> https://bugs.launchpad.net/ubuntu/+source/ruby1.8/...
> so I resend it here. Does someone have any clues on this ?

dup is a "shallow" copy. For a Hash, you'll get a new Hash but with the
keys and values pointing to the same objects.

>> h1 = {1=>"one", 2=>"two"}
=> {1=>"one", 2=>"two"}
>> h2 = h1.dup
=> {1=>"one", 2=>"two"}
>> h1.object_id
=> -605621648
>> h2.object_id
=> -605633988           #<< the hashes are different objects
>> h1[1].object_id
=> -605621708
>> h2[1].object_id
=> -605621708           #<< the values are the same object
>>

If you want a deep copy, you have to do it yourself.

Similarly, if you freeze a Hash, you are just freezing the Hash itself,
not all the objects it points to.

>> h1
=> {1=>"one", 2=>"two"}
>> h1.freeze
=> {1=>"one", 2=>"two"}
>> h1[2] << "xxx"
=> "twoxxx"
>> h1
=> {1=>"one", 2=>"twoxxx"}

If you want a "deep freeze" then you'll have to do it yourself.

Your test code looks rather more convoluted than it needs to be, so you
should be able to boil it down to a two or three line case which shows
you what's happening.

However I suggest you close the Ubuntu ticket though as 'invalid'

Regards,

Brian.
983428278161aebf0513417242794952?d=identicon&s=25 David Maciejak (Guest)
on 2009-06-09 12:30
(Received via mailing list)
Thanks for the details, in the end as you said I did the deep copy
myself. I will close the ubuntu entry.

david
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