On: What would it take to add refinement types to Rust...

[bonzini]

Is the former different from a hypothetical Result::Err type (I don't know if you'd spell that Result::Err<T> or Result::<T>::Err)?

[n_plus_1_acc → bonzini]

Different solutions to the same problem. Pattern types are more general than enum variant types.

[JoshTriplett → bonzini]

Same concept, but generalized to any type, not just enums.