sub pack {
        my $self=shift;
        my $record=join(':', @{$self}{keys %{$self->{_permitted}}});
        return $record;
  }

##</code><code>##

my @permitted=qw(name price description);
my %fields;
@fields{@permitted}=undef;

##</code><code>##

  sub pack {
        my $self=shift;
        my $record=join(':', @{$self}{@permitted});
        return $record;
  }