http://wiki.slowass.net/?PerlDesignPatterns Perl Design Patterns 非常好
http://search.cpan.org/~swalters/typesafety-0.04/typesafety.pm
http://search.cpan.org/~ggoebel/Class-Contract-1.14/lib/Class/Contract/Production.pm
http://wiki.slowass.net/?TypeSafety
http://dev.perl.org/perl6/rfc/95.html class object
http://perl.plover.com/yak/typing/