How up-to-date is "Looking into immutable data with Optics" from <@U0RM4EPC7> from two years ago?

# arrow

[CLOVIS]

How up-to-date is "Looking into immutable data with Optics" from @simon.vergauwen from two years ago?

[simon.vergauwen]

It's fairly up-to-date, but doesn't go super deep. The Optics library hasn't had a lot of change since it was first added in 2017.

[CLOVIS]

Thanks 👍

[CLOVIS]

So far I've gone through the basics of what @optic does to a data class, but I'm not sure how to jump from that to how to 'mutate' trees

[simon.vergauwen]

It doesn't mutate long story short, it composes function that together build a very complex copy that you would otherwise have to write by hand.

[CLOVIS]

Sorry, I understand it's all just copy, but I'm not sure how you get to actually doing it. We'll see if the video clears that up 🙂

[simon.vergauwen]

Ah, that is a bit harder to explain. It also depends heavily on which optic you compose together.

My original goal when I started building Arrow Optics (I named it Optikal at the time) was to understand how optics worked 🙃

[CLOVIS]

And… did you understand it? 😂

Am I right to expect that after writing this code:

@optics
data class Test(val name: String) {
	companion object
}

I should be able to type:

Test.name

or did I forget something?

[simon.vergauwen]

Yes, I understand it after building it 😄 Yes, you should but you need to setup KSP correctly. Can be a bit tedious.

https://arrow-kt.io/docs/optics/#step-3-add-the-plug-in-optional

https://kotlinlang.org/docs/ksp-quickstart.html#make-ide-aware-of-generated-code

[CLOVIS]

I think I didn't forget anything? https://gitlab.com/clovis-ai/advent-of-code-2022/-/blob/master/build.gradle.kts

[CLOVIS]

Ah, my KSP is too old.

[CLOVIS]

Manually adding the generated files to the source files doesn't seem to be necessary anymore

[CLOVIS]

Optics do not work on private classes?

[simon.vergauwen]

Oh, interesting. No it's impossible to generate code for a private (file) class.

[simon.vergauwen]

Since it goes in a different file

[CLOVIS]

KSP is actually generating Kotlin code? I thought it generated bytecode directly

[CLOVIS]

I guess that's why everyone is waiting for compiler plugins 🙂

[CLOVIS]

nevermind, adding the generated source sets is still necessary