I'm able to call a function using async when its returning just one value.
However, if the return is a Pair, I get - Destructuring declaration initializer of type Deferred<Unit> must have a 'component1()' function
Am I missing something?
Here is a sample code:
import kotlinx.coroutines.async
import kotlinx.coroutines.runBlocking
fun main() = runBlocking {
val num = 11
val a = async { oneValue(num) }
println(a.await()) // returns 22
// This doesn't compile
val (b, c) = async { twoValues(num) } // Destructuring declaration initializer of type Deferred<Unit> must have a 'component1()' function
println(b.await())
println(c.await())
// Same code works without async-await
val (d, e) = twoValues(num)
println(d)
println(e)
}
suspend fun oneValue(num: Int): Int {
return num * 2
}
suspend fun twoValues(num: Int): Pair<Int, Boolean> {
return Pair(num * 2, true)
}
The problem is that you can only destructure the Pair this way, but not the Deferred itself.
You could first assign the deferred value to a single variable, and later await it so you get a Pair that you can destructure:
val deferredPair = async { twoValues(num) }
// do other stuff concurrently
val (b, c) = deferredPair.await()
println(b)
println(c)
If you don't really need to do anything concurrently with this twoValues(), you could also just call it directly (as you did in your last example):
val (b, c) = twoValues(num)
println(b)
println(c)
Note that here your suspend function does its whole computation and then returns the Pair of the 2 computed things. It doesn't offer the possibility to await parts of it. This is probably what you're looking for, so it should be OK.
If you needed to have 2 independent computations that you could await independently, you would need to launch 2 coroutines instead, which would complicate things a bit. Most likely if this is what you want, the computations are likely independent enough to be put into 2 different suspend functions which you can call in 2 separate async (so you're back to the known situation of having a single return value).