use strict;
use Clone qw(clone);

my $foo = foo->new();
$foo->{spam} = {spam =>'eggs'};

my $bad_clone  = $foo->new();
my $good_clone = clone($foo);

$bad_clone->{spam}->{spam}  or warn "bad has no eggs";
$good_clone->{spam}->{spam} or warn "good has no eggs";

package foo;
use strict;

sub new {
   my $class = shift;
   my $proto = ref($class) || $class;
   return bless {}, $proto;
}