See Class::MakeMethods for general information about this distribution.
See Ref for the original version of the clone and compare functions used above.
See Clone (v0.09 on CPAN as of 2000-09-21) for a clone method with an XS implementation.
The Perl6 RFP #67 proposes including clone functionality in the core.
See Data::Compare (v0.01 on CPAN as of 1999-04-24) for a Compare method which checks two references for similarity, but it does not provide positive/negative values for ordering purposes.