|Perl: the Markov chain saw
Another object idiom: this one, people tell me is aweful. I like it a lot because it overcomes something I hate about Perl: how object instance data requires lots of funny syntax. This syntax makes it tedious to refactor code from a subroutine into a method. Like Abagail's, it uses lexicals to good effect. It requires some glue, but class fields are then normal lexical variables. The object is a blessed hash - but instead of data, the hash holds the methods. The AUTOLOAD glue just dispatches to the correct hash element. The glue sets $self, so it is not necessary to read it off of the argument list manually, should it be needed (for a method call, for example).
Primary drawbacks are a small speed penalty - but for very small data classes like this, I tend to use rather ordinary blessed arrays, anyway, or psuedohashes, or "use fields" pragmatic module (all about the same thing right now - psuedohashes will be going away I'm told). Code inheritance works - however, fields declared lexically like this aren't inherited. All data is essentially private. I find this just as well - it forces a subclass to use its parents accessors. Finally, you have to be somewhat accustomed to Functional Programming to be used to staring at indenting like that. This is just a brief restatement of the second half of Anonymous Subroutine Objects at PerlDesignPatterns.com. I treat the AUTOLOAD footer as a Wrapper Module, and just use it into my namespace.