> Every object is (or at least should be) "a description of what to do" in the exact sense you're using here. This is crucial to understand for properly using O

> Every object is (or at least should be) "a description of what to do" in the exact sense you're using here. This is crucial to understand for properly using OOP. I think you may have missed the point. In most OOP languages, an object exposes some capabilities (methods that can be called, properties that can be read, etc), but it does not describe itself very well at all. This is why we have RTTI, instanceof etc. to switch on what an object is. Alternatively, we can use the visitor pattern. As the OP states, these are not as elegant as DUs and matching.