“Can you make a query bus with SimpleBus?” The question has been asked many times. I’ve always said no. Basically, because I didn’t build in the option to return anything from a command handler. So a handler could never become a query handler, since a query will of course have to return something.

I’ve always thought that the demand for a query bus is just a sign of the need for symmetry. If you have command and query methods, then why not have command and query buses too? A desire for symmetry isn’t a bad thing per se. Symmetry is attractive because it feels natural, and that feeling can serve as design feedback. For instance, you can use lack of symmetry to find out what aspect of a design is still missing, or to find alternative solutions.