This is not the way XML::Simple works. XML::Simple is designed to let you input an XML file (with some restrictions) and use the data it contains or update it and output it back. Altough I have never tried it I would bet it will not output arbitrary data structures as XML (although that might be fun!).

On the other hand XML::Dumper and Data::DumpXML will dump data to XML. I have no idea how fast they are though (and considering Data::DumpXML is also written by Gisle AAs I don't think it will be faster than Data::Dumper).

Directly from the XML::Simple docs:

XMLout()

Takes a data structure (generally a hashref) and returns an XML encoding of that structure. If the resulting XML is parsed using XMLin(), it will return a data structure equivalent to the original.

That sounds similar to what Data::Dumper is being used for here.

You are actually right, although I don't really like how XML::Simple saves data structures.

Here is an example of what XML::Simple and XML::Dumper can do:

#!/bin/perl -w
use strict;
use XML::Simple;
use XML::Dumper;

my $struct= { toto => [1,2,3],
              tata => "duh",
              tutu => { tutu_toto => 1, tutu_tata => 2 },
             };

my $out= XMLout( $struct); 
print "XML::Simple: $out\n";

my $dump = new XML::Dumper;
print "XML::Dumper: ", $dump->pl2xml( $struct);
[download]

The result is:

XML::Simple: <opt tata="duh">
  <tutu tutu_tata="2" tutu_toto="1" />
  <toto>1</toto>
  <toto>2</toto>
  <toto>3</toto>
</opt>

XML::Dumper: <perldata>
 <hash>
  <item key="tata">duh</item>
  <item key="tutu">
   <hash>
    <item key="tutu_tata">2</item>
    <item key="tutu_toto">1</item>
   </hash>
  </item>
  <item key="toto">
   <array>
    <item key="0">1</item>
    <item key="1">2</item>
    <item key="2">3</item>
   </array>
  </item>
 </hash>
</perldata>
[download]

I personnaly think the XML::Dumper way is cleaner but YMMV