So, effects and the unaryPlus have been removed. H...

# compose

[Neal Sanche]

So, effects and the unaryPlus have been removed. How would the following code be rewritten to follow the latest fashion in Compose? I think it was originally written in an article by @Luca Nicoletti and doesn't compile anymore on Dev04:

// general purpose observe effect. this will likely be provided by LiveData. effect API for
// compose will also simplify soon.
fun <T> observe(data: LiveData<T>) = effectOf<T?> {
    val result = +state<T?> { data.value }
    val observer = +memo { Observer<T> { result.value = it } }

    +onCommit(data) {
        data.observeForever(observer)
        onDispose { data.removeObserver(observer) }
    }

    result.value
}

Ref: https://medium.com/swlh/android-mvi-with-jetpack-compose-b0890f5156ac

[Adam Powell]

Change = effectOf<T?> to, : T? in the signature (normal return value) and add @Composable as a function annotation, then remove the `+`s from the effect calls in the function body and add an explicit return keyword at the end. Change memo to remember as it was renamed.

[Zsolt]

https://gist.github.com/zsoltk/94a3c865c092fcca0d55bb096d9c8345

[Adam Powell]

yep, that. ☝️

[Neal Sanche]

Nice I was so close... just had the return statement wrong. Will try that out, thanks guys.

[Adam Powell]

the syntax change also removes the weirdness around operator precedence that made these not work so well as extension functions or properties; you could just as easily declare this as,

@Composable
val <T> LiveData<T>.latestValue: T? get() { ... }

if you'd prefer.

[Neal Sanche]

I like that too. And, I nearly immediately run into an Exception during code generation.

e: java.lang.IllegalStateException: Backend Internal error: Exception during code generation
Element is unknownThe root cause java.util.NoSuchElementException was thrown at: androidx.compose.plugins.kotlin.compiler.lower.ComposableCallTransformer.irComposableExpr(ComposableCallTransformer.kt:1362)

Caused by: java.util.NoSuchElementException: Collection contains no element matching the predicate.

I guess I'll go on a hunt for what might be causing that.

[Neal Sanche]

ViewModel uses a coroutine flow. That seems to be the root cause for me. Got way more information once I added

composeOptions {
        kotlinCompilerVersion "1.3.61-dev-withExperimentalGoogleExtensions-20200129"
        kotlinCompilerExtensionVersion "0.1.0-dev04"
    }

Into my build.gradle.

[Neal Sanche]

I was able to get things working without any coroutines. Can't wait for full coroutine support in the compiler extensions.