Passing additional arguments to XML::Twig handlers

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

Wise Monks: I'm using XML::Twig and its function handlers. These take coderefs, to which are passed (as @_) the values of the twig and the section being processed. However, if I want to pass the coderef other values as well, it doesn't seem to retrieve the twig and section as I'd expect. I'm a bit stumped, I can't seem to find this case in the documentation. Example:

#!/usr/bin/perl
use XML::Twig;
my $t=XML::Twig->new( twig_handlers => { name => \&my_s });
$t->parse('<doc><name>Alice</name><name>Bob</name></doc>');

sub my_s {
    my ($twig, $section, $greeting) = @_;
    print $greeting || "Hello" , ", ", $section->text(), "!\n";
}

# Yields:
# Hello, Alice!
# Hello, Bob!
[download]

If I try

my $t=XML::Twig->new( twig_handlers => { name => \&my_s("Hi") });
# Can't call method "text" on an undefined value
# likewise with &my_s->("Hi")
[download]

What am I missing?

Comment on Passing additional arguments to XML::Twig handlers Select or Download Code

Replies are listed 'Best First'.
Re: Passing additional arguments to XML::Twig handlers by Fletch (Bishop) on Jan 29, 2008 at 14:31 UTC
Use an anonymous coderef (which adds the extra arguments) to set the handler. `my $t = XML::Twig->new( twig_handlers => { name => sub { my_s( @_, "Hi +" ) } } );` [download] The cake is a lie. The cake is a lie. The cake is a lie.	[reply] [d/l]
Re^2: Passing additional arguments to XML::Twig handlers by pseudomonas (Monk) on Jan 29, 2008 at 14:45 UTC
Thanks! This seems to work fine.	[reply]
Re: Passing additional arguments to XML::Twig handlers by mirod (Canon) on Jan 29, 2008 at 14:43 UTC
The best explanation I have seen about closures and how to use them in XML::Twig is Simon Cozens' Achieving Closure.	[reply]
Re: Passing additional arguments to XML::Twig handlers by moritz (Cardinal) on Jan 29, 2008 at 14:33 UTC
If you want only constant args, you can fall back on closures: `my $greeting = "hi"; my $my_s = sub { my ($twig, $section) = @_; print $greeting \|\| "Hello" , ", ", $section->text(), "!\n"; }` [download] You can then pass the closure in `$my_s` just like a normal reference to a sub.	[reply] [d/l] [select]
Re^2: Passing additional arguments to XML::Twig handlers by pseudomonas (Monk) on Jan 29, 2008 at 14:47 UTC
The args change from parse to parse, unfortunately. Closures are something I need to get more used to in general, though - thanks!	[reply]