sub iterative_copy {
   my $root;
   my @todo;

   push @todo, [ $_[0], \$root ];

   while (@todo) {
      my ($src, $dst) = @{ shift(@todo) };

      if (not ref $src) {
         $$dst = $src;
      }
      elsif (ref $src eq "HASH") {
         $dst = ($$dst = {});
         push @todo, map { [ $src->{$_}, \($dst->{$_}) ] } keys %$src;
      }
      elsif (ref $src eq "ARRAY") {
         $dst = ($$dst = []);
         push @todo, map { [ $src->[$_], \($dst->[$_]) ] } 0..$#$src;
      }
      else {
         Carp::croak "What's a " . ref $_ . "?" 
      }
   }

   return $root;
}