A very general approach:

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__
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$ perl -l
use foo;
use strict;
use warnings;

my $foo = foo::->new();
$foo->data('bar', 42);
print $foo->data('bar');
__END__
bar
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Update: Added to make a complete working sample.