Very nice!

The additional, always-ignored nil into Fiber.yield is because Fiber.yield has very similar behavior to next, and implicitly unwraps arrays of size 1 if that's the only arg given.

As for the performance concern, I actually don't think there's any additional array unwrapping. In the previous code, there was:

@result = object.__send__ method, *args do |*vals|
ret = Fiber.yield(*vals)

so that splat into Fiber.yield(*vals) was previously doing the array unwrapping. In the new code, the vals array is passed straight through Fiber.yield(vals, nil) and returned from next_values to finally be unwrapped in next. So it should be the same number of allocations and unwraps.

I could imagine some performance degradation due to the additional call, tho, since next now calls next_values. I did not attempt to benchmark this change.

I did not attempt to benchmark this change.

You are right... there's already a lot of argument array-juggling so if anything has changed it's probably a lateral move. I have not benchmarked this code much at all so it's an open project to investigate that (and likely the hottest pieces would need to move to Java code to improve performance).

Thanks for the fix!

I'm thrilled to give back. Thanks for all your hard work on JRuby, it's a fantastic project.