That's great! Are you making the argument that I won't be able to find an example where doing some transform in a type-safe way is awkward in TypeScript, or just that this one example can be done in TypeScript?

By the way, my example was meant to be more like User -> User where there are some string values and some other types of value. You want to do the transformation in a generic way, but still have the type-safe object come out the other end with all the expected keys.