How to create diff of two generic T:Codable structs in Swift?

Question

Given: I have two structs of the same type, conforming to Codable Protocol. The structs can be multi-level (nested properties, surely also are conforming to Codable). The type is not known at the time of implementation, so i consider it generic, conforming to Codable.

One object is "base" (say, received from server), second (actually the copy of "base"), but modified inside application.

The intention is: To send a request for saving new data, but sending only the "diff" of two structs. So, only the fields, that are different should be present in resulting JSON.

The straightforward way with getting JSON strings for both structs and manipulating with them, is understandable, but seem to be the last-chance approach...

I've tried the approach with Mirror, and recursion, but now have managed to make it work only for first level - on the second level of nesting i've lost the type of nested property (if struct or array), and cannot cast it right then...

I wonder if it can be made somehow with custom encoder?

P.S.: the generic type should have all properties as Optionals, so should not provide any explicit initializers.

Answer 1

Instead of your "last-chance approach" -- matching JSON strings -- you could use JSONSerialization.jsonObject to convert the JSON data to Foundation objects and perform your comparison on that higher level of abstraction (if that's what you meant in your question in the first place, then sorry - nevermind).

Of course you'd pay an extra penalty of converting your Codable objects to data and then parsing that data into an object hierarchy.