package File::With::State;
use strict;
use warnings;
use Scalar::Util qw( refaddr );
use base 'IO::File';

my %stash;  # hold inside-out state

sub new {
    my $class = shift;

    # create the object and rebless
    my $self = IO::File->new();
    bless $self, $class;

    # initialize the object
    $stash{ refaddr $self } = {};
    $self->open( @_ ) if @_;

    return $self;
}

sub stash {
    my ($self, $key, $value) = @_;
    return unless $key;
    $stash{ refaddr $self }{ $key } = $value if $value;
    return $stash{ refaddr $self }{ $key };
}

# Note: this simple example is not thread-safe and also
# needs a destructor to avoid leaking memory

##</code><code>##

my $fh = File::With::State->new( 'some_file' );
my @lines = <$fh>;
$fh->stash( line_count => scalar @lines );