There is the currently experimental kotlinx.serialization library that generates e.g. JSON codecs at compile time. Not sure if that fits the bill.

Looks like it's doing annotation processing at compile time? The trouble with that is that you end up with "magic" code like calling methods that don't appear to exist, and in order to be able to work on the serialisation itself (e.g. to add a new format) you have to understand the "magic", because there isn't a good intermediate abstraction. The great advantage of Shapeless is that all the "magic" is in the library itself and it spits out a generic representation of your data classes in record form; you can implement a new serialisation format in 100% vanilla Scala without having to worry about any macros or annotations or anything.

It's not annotation processing, it's a compiler plugin with IDE support. So pretty deeply integrated. It avoids some of those issues.

The kotlinx.serialisation design is pretty nice. It's basically what you describe. The compiler generates generic code that can call into a variety of "codecs" but they don't have to actually be serialisation specific. So there are codecs for JSON, protobufs, CBOR etc but you can also do arbitrary object graph transformations with the framework. A deep clone being a simple hello-world type example. I've never used Shapeless but it sounds pretty similar in some ways.

https://github.com/Kotlin/kotlinx.serialization

> It's basically what you describe. The compiler generates generic code that can call into a variety of "codecs" but they don't have to actually be serialisation specific. So there are codecs for JSON, protobufs, CBOR etc but you can also do arbitrary object graph transformations with the framework. A deep clone being a simple hello-world type example.

So what does the value that gets passed into your codec look like? What makes Shapeless tick is that it can represent records generically at the type level; records will have a type like

    type Book = 'author ->> String :: 'title ->> String :: HNil

that you can actually break down and do meaningful operations on (e.g. you could run it through a function that counts the lengths of strings and get something of type 'author ->> Int :: 'title ->> Int :: HNil, in a fully type-safe way). I'd be impressed if someone managed to encode those kinds of types into Kotlin - e.g. I don't think Kotlin has singleton types, so being able to compare field names at the type level is probably impossible?