Re: Passing data to XML::Twig twig_roots callbacks....?

So this code runs, but obviously doesn't pass my data. It loops the
expected number of times, given the XML it is parsing:

sub get_grandchild_info {
  my hash_ref = shift();
  return sub {
    my ($twig, $element) = @_;
    #blah blah, do something print-y here
  }
}

my $xmltwigobj = XML::Twig->new(
     twig_roots => {
       'Information/Child/Grandchild' =>
       get_grandchild_info,
     }
);

If I change the object instantiation code to what immediately
follows, my subroutine executes precisely 1 time only:

sub get_grandchild_info {
  my hash_ref = shift();
  return sub {
    my ($twig, $element) = @_;
    #blah blah, do something print-y here
  }
}

my $xmltwigobj = XML::Twig->new(
     twig_roots => {
       'Information/Child/Grandchild' =>
       get_grandchild_info(),
     }
);

And finally this version does the same thing, executing just the
first time the subroutine is "instantiated" - a term I'll use
lightly since I believe this is technically a closure-utilizing
callback, not an object:

sub get_grandchild_info {
  my hash_ref = shift();
  return sub {
    my ($twig, $element) = @_;
    #blah blah, do something print-y here
  }
}

my $xmltwigobj = XML::Twig->new(
     twig_roots => {
       'Information/Child/Grandchild' =>
       get_grandchild_info($self),
     }
);

I'm guessing there's something wrong with the prototype for my
subroutine so $smltwigobj isn't really connecting with
get_granchild_info when I change the number of args... the question
is (a) why? and (b) how to fix that?


Jenda Krynicky wrote:
> From: Dustin Suchter <[email protected]>
>> I'm having a hard time wrapping my brain around the idea of using
>> twig_roots with twig_handlers (specifically so I can pass data back
>> and forth) in order to process large XML files. Perhaps I'm missing
>> something obvious, and hopefully someone can help!
>>
>> I've got a large XML file currently parsed cleanly using twig_roots
>> and setting callbacks on various elements:
>>
>> my $xmltwigobj = XML::Twig->new(
>>     twig_roots => {
>>         'Information/Child/Grandchild' => \&get_grandchild_info,
>>     }
>> );
>>
>> sub get_grandchild_info {
>>     my ($twig, $element) = @_;
>>     #blah blah, do something print-y here
>> }
>>
>> My problem is that I'd like to store the info I parse via
>> get_grandchild_info somewhere useful, where "useful" is not (a) in a
>> global or (b) printed somewhere. Specifically, I'd like to pass the
>> reference to a DBM::Deep object to get_grandchild_info and have any
>> new info added to the existing DBM::Deep object, but really we
>> shouldn't need to be specific, I just want something like:
>>
>> sub get_grandchild_info_extra {
>>     my ($twig, $element, $hash_ref) = @_;
>>     #awesomeness
>> }
>>
>> I found Question 27 at
>> http://xmltwig.com/xmltwig/XML-Twig-FAQ.html#Q27 to be pretty spot-on
>> for my needs in terms of data passing, but in the end it didn't help
>> me since nobody seems to use the twig_roots parsing methodology in
>> combination with the 'closures' mentioned there (which smell a lot
>> like globals to me anyway...).
>>
>> I'd love to see an example of how to modify my code, above, to allow
>> me to pass a 3rd argument to my callback subroutine.
> 
> sub get_grandchild_info {
> 	my hash_ref = shift();
> 	return sub {
>      my ($twig, $element) = @_;
>      #blah blah, do something print-y here
>    }
> }
> 
> ...
> 
> my $xmltwigobj = XML::Twig->new(
>     twig_roots => {
>         'Information/Child/Grandchild' => 
> get_grandchild_info(\%DBM_HASH),
>     }
> );
> 
> 
> 
> Sometimes a plain old global is the best solution though.
> 
> And sometimes it's better to have a look at a different module. Maybe 
> XML::Rules will end up being easier. Though that of course depends on 
> your XML and your needs.
> 
> XML::Rules will take care of remembering the data for you and if you 
> like you can instruct it to store the data of some tag in a DBM::Deep 
> hash:
> 
> 
> use XML::Rules;
> use DBM::Deep;
> 
> my $parser = XML::Rules->new(
> 	start_rules => [
> 		YourHugeTag => sub {
> 			my %temp = %{$_[1]};
> 			tie %{$_[1]}, 'DBM::Deep', $filename;
> 			%{$_[1]} = %temp;
> 			1;
> 		}
> 	],
> 	rules => [
> 		...
> 
> (or if the tag doesn't have any attributes you'd be interested in
> 
> 
> my $parser = XML::Rules->new(
> 	start_rules => [
> 		YourHugeTag => sub {
> 			tie %{$_[1]}, 'DBM::Deep', $filename;
> 			# and maybe 
> 			# %{$_[1]} = (); 
> 			# to clear the hash
> 			1;
> 		}
> 	],
> 	rules => [
> 		...
> 
> And now all the data returned by the rules specified for the child 
> tabs of YourHugeTag  will be stored in the DBM::Deep and be available 
> in $_[1] within the rule specified for YourHugeTag.
> 
> 
> Jenda 
> ===== [email protected] === http://Jenda.Krynicky.cz =====
> When it comes to wine, women and song, wizards are allowed 
> to get drunk and croon as much as they like.
> 	-- Terry Pratchett in Sourcery
> 
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