[alpinisme]

The same point holds of interfaces. And it’s not clear what the alternative is. No type system I’m aware of would force you to change all occurrences of this business logic pattern, with or without ad hoc polymorphism.

But at least ad hoc polymorphism lets you search for all instances of that business logic easily.

[ogogmad]

ML languages have a "types, modules, types-of-modules, and functors" approach to ad-hoc poly. It's a bit strange compared to what other languages do. I am wondering whether it's ever been seen outside of SML and OCaml.

For JSON deserialisation, you would declare a module-type called "JSON-deserialiser", and you would define a bunch of modules of that module-type.

The unusual thing is that a JSON-deserialiser would no longer be tied to a type (read: type, not module-type). Types in ML-like languages don't have any structure at all. I suppose you can now define many different JSON-serialisers for the same type?