Asp Forum - ruby dup unexpected behaviour

David Maciejak

6/9/2009 9:52:00 AM

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()

2 Answers

Brian Candler

6/9/2009 10:20:00 AM

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.
--
Posted via http://www.ruby-....

David Maciejak

6/9/2009 10:29:00 AM

Thanks for the details, in the end as you said I did the deep copy
myself. I will close the ubuntu entry.

david

On Tue, Jun 9, 2009 at 12:20 PM, Brian Candler<b.candler@pobox.com> wrote:
> 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 =3D {1=3D>"one", 2=3D>"two"}
> =3D> {1=3D>"one", 2=3D>"two"}
>>> h2 =3D h1.dup
> =3D> {1=3D>"one", 2=3D>"two"}
>>> h1.object_id
> =3D> -605621648
>>> h2.object_id
> =3D> -605633988 =A0 =A0 =A0 =A0 =A0 #<< the hashes are different objects
>>> h1[1].object_id
> =3D> -605621708
>>> h2[1].object_id
> =3D> -605621708 =A0 =A0 =A0 =A0 =A0 #<< 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
> =3D> {1=3D>"one", 2=3D>"two"}
>>> h1.freeze
> =3D> {1=3D>"one", 2=3D>"two"}
>>> h1[2] << "xxx"
> =3D> "twoxxx"
>>> h1
> =3D> {1=3D>"one", 2=3D>"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.
> --
> Posted via http://www.ruby-....
>
>

comp.lang.ruby

ruby dup unexpected behaviour

David Maciejak

Brian Candler

David Maciejak

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