Optics based on kotlin.reflect

[serras]

The issue #2418 (by @magneticflux-) has given me an idea for an API for optics based on KProperty. It's a bit rough on the edges (for example, there's no way to check at compile-time that you are referring to a field in a data class, so the access may fail at runtime). On the other hand, it allows you to create optics easily for types you do not control:

data class Person(val name: String, val age: String, val friends: List<Person>)

val friendNames = Person::friends.every compose Person::name.lens
friendNames.modify(someFriends) { it.capitalize() }

The prism part is done using a combinator instance<Parent, Children>. Maybe a better name is needed, though.

[nomisRev]

As a rule Arrow never exports unsafe functions from the main APIs.
I was hoping to solve this issue with a compiler plugin, but they've been on hold for a long time since Optics was released.
Soon they might become stable though, and creating optics for classes you don't own will be automatically solved as a part of that.

With that in mind, that'd also mean we'd have to deprecate this.
We could try looking into doing this with Reflekt though.

[nomisRev]

Or perhaps in a second module arrow-optics-reflect so it can be opted-in.

[serras]

Or perhaps in a second module arrow-optics-reflect so it can be opted-in.

I can do that, sure. The goal here was to provide a simple bridge which works for now.

[nomisRev]

Yes, that makes perfect sense. We've historically done that in other projects too, there is a small reflection based module in Arrow Endpoints for Schema too but hopefully we can replace all those with nicer plugins next year 🥳

Thanks for adding this! When moved to arrow-optics-reflect, and perhaps a small addition in the docs we can merge 👍

[serras]

@nomisRev I've just pushed a commit which moves this to a new arrow-optics-reflect package. If you think it's OK there, I can move on and write some documentation.

[nomisRev]

Yes, that looks perfect @serras! Thanks for moving it 👍
Some docs would be great too ❤️

Let me know when you think this is ready, and I'll review and ✔️

[nomisRev]

So this exposes the API of Kotlin Std, and uses the JDK8 implementation?

I'm still not a 100% sure how this works, and what is the correct config :/
I don't we're doing different things in different modules.. but off-topic for this PR.

[serras]

I'm not sure 100% either. In any case, I've removed the api dependency on stdlibCommon and just left the implementation for the JDK version.

[nomisRev]

@serras should become green after merging main.