Treat optionals as JSON.null to remove all the explicit unwrapping #4
Description
The thing you present primarily looks ugly because of the optional chaining at every single step:
if let street = json.person?.address?[0].street.stringValue { }
But it doesn't have to be like that (it is dynamic anyways). I think you could improve that a lot by essentially adding "nil messaging":
if let street = json.person.address[0].street.stringValue { .. }
Instead of returning an optional in every item of the chain, only make the leaf accessors (stringValue, intValue, etc) optional. When a lookup is not successful, return JSON.null (which itself returns JSON.null on all JSON accesses, so that the result propagates).
If you'd like you could also add a JSON.lookupError(parent, key) as a result for missed lookups for debugging purposes (and which also propagates down the call chain, and could even persist the lookup path from the root of the first lookup failure).