That's an interesting situation. A possible solution would be to let your subclass have its own private table of instances, and use the scalar reference as a key to that table, as such:

package MyDoc;
@ISA = qw(XML::LibXML::Document);

my %instance_hashes;

sub new {
  my $class = shift;
  my $self = $class->SUPER::new('1.0', 'UTF8');

  my @listeners = ();

  # initialize private hash data
  $instance_hashes{$self} = {};

  $self->listener(\@listeners);
  bless $self, $class;
}

# accessor / mutator
sub listener {
  my $self = shift;

  if (@_) {
    $instance_hashes{$self}{Listeners} = shift;
  }

  return $instance_hashes{$self}{Listeners};
}
[download]

Here we use the $self reference as the key to %instance_hashes, where we can store info about each instance.

BTW, please use <code></code> tags in your posts. Also, I changed the line where you set the Listeners to @listeners. The way you had it (in scalar context), it would initialize $self->{Listeners} to the size of @listeners, not the elements of the list. Use a reference to the @listeners array to allow access to it from other methods, which is probably what you had in mind.

blokhead