my $obj = Foo->new( sort => 1);

  ...

while (my $val = $obj->next) {

##</code><code>##


if ($self->{sort}) {
    @out = (ref($self->{sort}) eq 'CODE') ?
                       (sort {&{$self->{sort}}($a,$b)} @out) :
                       (sort @out);
}