package Encoder;

## Basic constructor
sub new {
   my $type = shift;
   my $self = {};
   bless $self, $type;
}

## Define the common interface
sub shared_stuff { return reverse $_[1]; }

## Define the uncommon interface
sub other_stuff { 
   die "Somebody didn't define the other stuff!"; 
}

## Generalized encoding method
sub encode {
   my $self = shift;
   my ($text) = @_;

   $self->common_stuff($text);
   $self->other_stuff($text);
}

##</code><code>##

# In Encoder/B.pm
package Encoder::B;

use base 'Encoder';

sub other_stuff {
   my ($text) = @_;

   my $new_text = $text;
   $new_text =~ s/a/c/g;
}

##</code><code>##

use Encoder::B;
use Encoder::Whatever;

our %Encoder_Table => (
    'b' => 'Encoder::B',
    'c' => 'Encoder::Whatever',
);

sub encoder_factory {
  my ($e) = @_;

  exists $Encoder_Table{$e} 
    or die "'$e' is not a valid type of encoder, sorry!";

  return $Encoder_Table{$e}->new();
}


##</code><code>##

my $encoder = encoder_factory($whatever_e_is);
print $encoder->encode("Hahahaha!");