my $x = My->new(source=>"xml");
my $y = My->new(source=>"json");

##</code><code>##

package My::XML;
use My;
our @ISA = qw[My];

sub init {...}

1;

package My::JSON;
use My;
our @ISA = qw[My];

sub init {...}

1;

package My;

sub new {
    my $class = shift;
    my $self = bless {}, $class;
    $self->init;
    $self;
}

1;

package main;
use My::XML;
use My::JSON;

my $x = My::XML->new;
my $y = My::JSON->new;