I'm not the biggest fan how the casting is working here. We have various different structures we can send through now but they all need to be cast down and then manually cast back up. I think I'd rather have the base structure done as union then. But if we're going this far, why now consider going a little farther with this. The transaction events are handled in a loop but don't seem to require anything from the context of the loop. So there is no reason that they can't be reimplemented as callbacks. And instead of having one callback function which does everything, we can introduce one for each of kind of event. The transaction can be seeded with a structure pointing to all the various callbacks. Then we start treating a transaction like an event loop. This would improve type safety since we don't have to cast anything anymore. This would improve readability since we don't have to rely on casts and heavy switch statements. Just an idea. Back on topic, I do like this change.