zuma53 has asked for the wisdom of the Perl Monks concerning the following question:

Hi--

I've been using $foo->paste('last_child', $bar) to graft subtrees onto a larger tree and it's been working as expected. That is, the paste will *copy* the contents of foo onto bar.

Now, it seems that the paste is using a pointer of foo to the bar tree. Since foo is populated within a loop with a "new" for foo at the start of the iteration, each time the new is hit, the contents of the prior foo (now attached to bar) vanishes. What persists on bar is only the value of foo.

Strangely, the population of the nodes within foo is done via the same paste/last-child mechanism, but this works as expected.

Can someone clarify this? Or am I doing something wrong? Thanks. 

use XML::Twig;

my $objectsTwig = new XML::Twig;
$objectsTwig->parse('<objects />');

$OBJECTS_ROOT = $objectsTwig->root;

do {
    my $object = new XML::Twig;
    $object->parse('<object />');
    $OBJECT_ROOT = $object->root;
    
    ... Add elements to <object> node
    
    $OBJECT_ROOT->paste('last_child', $OBJECTS_ROOT);
        
}  until (yada...);

[download]

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Re: XML-Twig paste
by Anonymous Monk on Oct 16, 2012 at 20:01 UTC
    Processing XMl efficiently with XML::Twig - Section 4 shows this that works 
     #!/usr/bin/perl --
use strict; use warnings;
use XML::Twig;
my $objectsTwig = XML::Twig->new;
$objectsTwig->xparse('<objects />');
print $objectsTwig ->toString, "\n";
my $OBJECT_ROOT = $objectsTwig->root;
for( 1 .. 10 ){
    XML::Twig::Elt->new(
        'object'
    )->paste(
        'last_child',
        $OBJECT_ROOT
    );
}
print $objectsTwig ->toString, "\n";
__END__
<objects/>
<objects><object/><object/><object/><object/><object/><object/><object
+/><object/><object/><object/></objects>

    [download]

    A root on the other hand seems doesn't like to be cut/paste while it is a root 

    #!/usr/bin/perl --
use strict; use warnings;
use XML::Twig;
my $objectsTwig = XML::Twig->new;
$objectsTwig->xparse('<objects />');
print $objectsTwig ->toString, "\n";
my $OBJECT_ROOT = $objectsTwig->root;
for( 1 .. 10 ){
    my $object = XML::Twig->new;
    $object->xparse('<object />');
    my $orphan = $object->root;
    $object->set_root(undef); ### crucial
    $orphan->cut;
    $orphan->paste('last_child', $OBJECT_ROOT );
}  
print $objectsTwig ->toString, "\n";
__END__
<objects/>
<objects><object/><object/><object/><object/><object/><object/><object
+/><object/><object/><object/></objects>

    [download]

    Bug? Intended behaviour? I don't know , but doesn't seem too important to me :)

[reply]
[d/l]
[select]

      Yup, if you  warn  $root->cut; you'll get undef, naturally 

      sub cut
  { my $elt= shift;
    my( $parent, $prev_sibling, $next_sibling, $last_elt);

    # you can't cut the root, sorry
    unless( $parent= $elt->{parent}) { return; }

      [download]

      So whatever the reason is, its intended

[reply]
[d/l]
[select]

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