Dominus has some slides that may help on that.

You can do this with inside-out objects. See the File::Marker example in my YAPC::NA 2006 talk.

Class::InsideOut makes this even easier.

package My::File::Class;

use base 'IO::File';

use Class::InsideOut qw/public id register/;

public some_property => my %some_property;

sub new {
  my $class = shift;
  my $self = IO::File->new( @_ );
  register( bless $self, $class );
  return $self;
}

1;
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Use like this:

use My::File::Class;

my $obj = My::File::Class->new( "filename.txt" );

$obj->some_property("foo");
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Since filehandles are typeglobs, you can access its associated hash and stick stuff in it. For example,

sub set_foo { 
    my $self = shift;
    my $val = shift;

    ${ *$self }{foo} = $val;
}
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Update: I think you can also just say *$self->{foo} = $val; which is less ugly.