package foo;

use strict;
use warnings;

sub new {
	my $class = shift;
	my $self  = {};
	$self->{data}   = undef;
	bless ($self, $class);
	return $self;
}

# setter and getter
sub data {
  my ( $self, $attr ) = @_;
  $self->{'data'}->{$attr} = $attr if (defined($attr));
  return $self->{'data'}->{$attr};
}
1;
__END__