We're talking about C code that has refcounted objects, where you have to know ahead of time to add or remove a refcount before you call specific C functions. I

We're talking about C code that has refcounted objects, where you have to know ahead of time to add or remove a refcount before you call specific C functions. In Rust that would just be an Rc or an Arc, and the programmer would not need specific knowledge. Or a C function that either returns an existing object, or a new object that is incompletely initialized. If it is an existing object, you are required to call a second function to finish the initialization. And you’re just supposed to know about that requirement; it’s not documented anywhere. On the Rust side they decided to return an Either<EmptyObject, InitializedObject> instead, so that the programmer can directly see what is going on. They’re not saying that all Rust APIs are immediately easy to understand, only that they require less manually–written documentation because the constraints can be encoded into the type system.