Can a Doctype have a Derived/Calculated Field?

I want to add a derived field that is calculated from an expression referencing other fields. I didn’t see any explanation of this in the documentation on Field types. Is it possible?

Virtual fields are on their way in V14:
https://github.com/frappe/frappe/pull/14593

There was some discussion on how to custom-code it in earlier versions here but I don’t know if anyone got it to work: