use strict;
use Clone qw(clone);

my $foo = foo->new(5);
my $bar = clone($foo);

print $bar->id(), "\n";

package foo;
use strict;

sub new {
   my ($class,$id) = @_;
   my $self = {
      id => $id || 42,
   };
   return bless $self,$class;
}

sub id {
   my ($self,$id) = @_;
   return $self->{id} unless $id;
   $self->{id} = $id;
}