I have been trying to play around `state` in Compo...

# compose

[Wajahat Karim]

I have been trying to play around state in Compose dev15. So, if create a state like val numState by state { 0 }, and use this in any composable like Text, it works good and fine. On doing numState++, the Text updates. But, if I use some custom data class like this below code:
data class Point(val x:Int = 0, val y:Int = 0)
And using this class to create state like val pointState by state { Point(3,4) }, and now if I update this like pointState.x++, then the Composables using this state aren't recomposed and updated. I don't understand how am I supposed to use state?

[Adam Powell]

Only the state var itself is observable in the above, not the contents

[Wajahat Karim]

Yes, when I did it like var newPoint = pointState.copy(x = 3) and reassiging this to pointState = newPoint , then it worked. But I am confused on whether this is a good practice, considering if contents are some ArrayLists etc instead of simple x, y integers performance wise?

[Adam Powell]

It often depends. Persistent collections are a good way of keeping immutability while preserving scalable performance, e.g. https://github.com/Kotlin/kotlinx.collections.immutable

[Adam Powell]

mutableStateListOf for example creates a list backed by persistent collections

[Adam Powell]

on the other side of things if you use MutableState for properties of mutable objects, you do get snapshot isolation for thread safety, plus observability, but it does come with overhead beyond a simple Int property; we're working to keep it cheap enough to use frequently but it's not free 🙂

[Wajahat Karim]

So, instead of combining these lists in a wrapper data class, if I use simply mutableStateListOf and update it, then this will work?

[Wajahat Karim]

Agree. I was actually looking into MutableState last night and will definitely experiment with it today to see if it solves my problem.

[Adam Powell]

so your point example could become:

@Stable
class Point(x: Int, y: Int) {
  var x by mutableStateOf(x)
  var y by mutableStateOf(y)
}

// usage; note 'remember' instead of 'state'
val point = remember { Point(1, 2) }

[than_]

There are tradeoffs (aren't there always? 🙂 ). Yes there is performance overhead on always creating new instances. But on the other hand you can easily check if the object changed without deep comparison. The performance overhead of creating new objects is mostly fine. Working with deep nested immutable data is unfortunately another beast 😕. For that I'd recommend this https://arrow-kt.io/docs/0.10/optics/dsl/

[Adam Powell]

yeah the arrow optics stuff is pretty slick. I don't think I'd recommend it to someone new to programming, but for someone comfortable with these concepts it's super handy

[Adam Powell]

mutable data does, as always, introduce the opportunity for different parts of the code to modify it outside of your expectations, so it's still good to prefer immutability unless you have a strong reason to make something mutable

[than_]

Oh for sure, there is a learning curve. But I believe its good (even for begginers) to know if there are solutions for your pain points 🙂

[Wajahat Karim]

Yeah. Arrow is defintily trickier. I will try to understand it. Also, I was looking at a callback loop from this snippet of you @Adam Powell https://gist.github.com/adamp/e69593c28fa8642bd7eee22bb4a733ee

I am unable to do this in dev15. Can you tell me how can I do this in dev15?

[Adam Powell]

right. I mention it because I do feel strongly that compose is something I could put in front of a first time programmer by the time we hit 1.0; once you get into more complex data flows the learning curve gets steeper

[Adam Powell]

@Wajahat Karim what about it isn't working?

[Adam Powell]

oh, the awaitFrame method was renamed to withFrameMillis iirc

[Wajahat Karim]

The awaitFrameMillis and lifecycleOwner are unresolved variables

[Adam Powell]

lifecycleOwner is a local variable, the whenStarted extension comes from the lifecycle-ktx library

[Adam Powell]

the LifecycleOwnerAmbient is still there, should just be an import

[Wajahat Karim]

It looks like awaitFrame is deprecated in dev15.

[Adam Powell]

you're looking for withFrameMillis

[Wajahat Karim]

Oh sorry, I got confused, You are right. Thanks a bunch 🙂