package Default;
use strict;

sub new {
	my $class = shift;
	my $self  = { };
	return bless $self, $class;
}

sub handle {
	my ($class, $text) = @_;
	return $text;
}

1;

##</code><code>##

package Upper;

use strict;
use Default;
use vars qw(@ISA);
@ISA = qw(Default);

sub handle {
	my ($class, $text) = @_;
	return uc($text);
}

1;

################################

package Lower;

use strict;
use Default;
use vars qw(@ISA);
@ISA = qw(Default);

sub handle {
	my ($class, $text) = @_;
	return lc($text);
}

1;

##</code><code>##

#!/usr/bin/perl -w
use strict;

use Default;
use Upper;
use Lower;

my $arg = shift || '';

my %handlers = (
	default => Default->new,
	upper   => Upper->new,
	lower   => Lower->new,
);

my $ref = $handlers{$arg} || $handlers{'default'};

print $ref->handle("AaAaAaAa"), "\n";