Don't have My inherit from My::XML and My::JSON, have My::XML and My::JSON inherit from My.

I'm guessing you want to do this since you get a file name and you want to load the file using the right module.

package My;

sub load {
   my ($class, %args) = @_;
   my $file_type = ...;
   if ($file_type eq 'xml') {
      require My::XML;
      return My::XML->new(%args);
   } elsif ($file_type eq 'json') {
      require My::JSON;
      return My::JSON->new(%args);
   }
}

sub new     { ... }
sub method1 { ... }
sub method2 { ... }
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