How to create an extension function with multiple receivers in Kotlin?-CodePudding

I want my extension function to have a couple of receivers. For example, I want function handle to be able to call methods of both CoroutineScope and Iterable instances:

fun handle() {
    // I want to call CoroutineScope.launch() and Iterable.map() functions here
    map {
        launch { /* ... */ }
    }
}

I thought this might work:

fun <T> (Iterable<T>, CoroutineScope).handle() {}

But it gives me an error:

Function declaration must have a name

I know that I can create the function with parameters, but

Is it possible to have multiple receivers for a single function and how to do that without parameters?

CodePudding user response：

As far as I know, this is currently impossible for types that we don't control. There are plans to add such feature, it is processed under KEEP-259.

I don't know what is the planned roadmap or when we could expect it to be added, but I hope we will see at least some previews this year.

CodePudding user response：

This is a very narrow case, but if your use case is that you have a higher order function where you want code in the lambda to have multiple receivers, and if the types you're wanting to combine are interfaces, you can create a class that wraps the interfaces as delegates. Within the lambda passed to the below function, you can call both Iterable and CoroutineScope functions.

class CoroutineScopeAndIterable<T>(
    private val coroutineScope: CoroutineScope,
    private val iterable: Iterable<T>
): CoroutineScope by coroutineScope, Iterable<T> by iterable

suspend fun <T> CoroutineScope.runSomething(
    iterable: Iterable<T>, 
    block: suspend CoroutineScopeAndIterable<T>.() -> Unit
) {
    CoroutineScopeAndIterable(this, iterable).block()
}