Cloning (weak) references

Tomte has asked for the wisdom of the Perl Monks concerning the following question:

In comp.lang.perl.misc it was asked (message-ID: <1109848552.496818.242290@o13g2000cwo.googlegroups.com>)

I've tried various cloning modules to clone a structure containing weak references.
use Storable 'dclone';
use Scalar::Util qw(weaken isweak);
my $x = 99;
my $y = [ \$x ] ;
weaken $y->[0];
$z = dclone $y;
print "y: ", isweak $y->[0];
print "z: ", isweak $z->[0];
[download]
This prints: y: 1 z: I've tried it using the Clone module and Clone::PP. Clone::PP does the same as Storable. Clone gives a segmentation fault. I'm using Perl 5.8.0 on Linux 2.4.20-8

my reply is

After a little bit of thought I'd say that's normal, to be expected behaviour: You're not cloning the weakend reference, but the the data it references, the reference in z[0], poiting to the clone of $x, is a completly new one, the data is cloned, not the reference. I may misunderstand the behaviour though...hmmm kind regards, Tom

Now I'm curious: Am I right? And if I'm right: Is it possible to clone references (Update preserving their "weakend-state")?

regards,
tomte

An intellectual is someone whose mind watches itself.
-- Albert Camus

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Re: Cloning (weak) references by hardburn (Abbot) on Mar 03, 2005 at 15:27 UTC
I think you're correct. To fix, the clone operation would have to ensure the ref count stays the same, but I don't think that is the right thing to do in the general case. Cloning means you have an extra something that is making a reference to your data, and that extra something means an additional ref count. "There is no shame in being self-taught, only in not trying to learn in the first place." -- Atrus, Myst: The Book of D'ni.	[reply]
Re: Cloning (weak) references by simonm (Vicar) on Mar 03, 2005 at 22:15 UTC
You could easily extend Clone::PP to do this, by adding a line to the `elsif ($ref_type eq 'REF' ...` section, something like `weaken( $copy = $source ) if isweak( $source );`.	[reply]

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