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?
In the Kotlin version 1.6.20 there is a new feature called Context receivers. This is a first prototype of context receivers. This feature allows to make functions, properties and classes context-dependent by adding context receivers to their declaration. There is a new syntax for that. In front of the function declaration we can specify a list of contextual types that would be required to invoke this function. A contextual declaration does the following:
The solution with context receivers looks like the following:
context(CoroutineScope)
fun <T> Iterable<T>.handle() {
map {
launch { /* ... */ }
}
}
someCoroutineScope.launch {
val students = listOf(...)
students.handle()
}
In the context(CoroutineScope)
we can declare multiple types, e.g context(CoroutineScope, LogInterface)
.
Since context receivers feature is a prototype, to enable it add -Xcontext-receivers
compiler option in the app's build.gradle
file:
apply plugin: 'kotlin-android'
android {
//...
kotlinOptions {
jvmTarget = "11"
freeCompilerArgs += [
"-Xcontext-receivers"
]
}
}