Did your experiment still do dynamic calls where Python would do dynamic calls? fastruby does not; all dynamic calls are converted into Java virtual dispatches,

Did your experiment still do dynamic calls where Python would do dynamic calls? fastruby does not; all dynamic calls are converted into Java virtual dispatches, which optimize and inline like normal Java code. The 30% improvement I got on "fib" was not as much as it would be for inferring the actual numeric types, but that's indeed possible here too. You should also keep in mind that the resulting code was by definition as fast as Java code would be doing the same work (i.e. all boxed math) so anything not math-related would actually be Java speed too.