@glyph I agree the idea didn't age well (slicing etc). But my more superficial nitpick is ease of reading code in IDE. Telco had large codebase with three major protocol impls. There was a common interface/abstract base for lots of objects, and then all 3 protos had their subclass. When you troubleshot, you know you were in 1 given tree... yet in IDE you had to jump the hoop, since any follow-ref took you to the interface, and from there you had to chase the right subimpl.