package PRODUCT;
  use Carp; 

  use strict;
  use vars qw($AUTOLOAD);
    
    sub fields {
        return qw(data);
    }

  sub new { 
  my $product = shift; 
  my $class = ref($product) || $product; 
  my $self={};
  bless $self, $class;
  my %fields;
  @fields{$self->fields}=undef;
  $self->{_permitted} = \%fields;
  $self->{$_}=$fields{$_} for (keys %fields);
  return $self;
  }

  sub AUTOLOAD { 

  my $self = shift; 
  my $type = ref($self) 
              or croak "$self is not an object"; 
            
  my $name = $AUTOLOAD; 
     $name =~ s/.*://; #strip fully-qualified portions

  unless (exists $self ->{_permitted} ->{$name} ) { 
  croak "Can't access `$name' field in class $type"; 
  } 


  if (@_) { 
     return $self -> {$name} = shift; 
     }else{
        return $self-> {$name}; 
        
      }  

  }

  sub DESTROY {}

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

package SUBPRODUCT;

use vars qw(@ISA);

@ISA=qw(PRODUCT);

sub fields {
        return qw(name price description);
}

1;