How do I return a value from a flow? Trying to ret...

# coroutines

[voben]

How do I return a value from a flow? Trying to return the myString value

suspend fun doSomething(): String {
   val myFlow = flow { emit("hello") }
   myFlow.collect { myString ->
        return myString
   }
}

[Mark Murphy]

Are you guaranteed that the Flow will emit one item? Or are you looking to return the first emitted item?

[voben]

Looking to return the first item emitted

[Mark Murphy]

You could use the first() operator: https://klassbook.commonsware.com/lessons/Flows%20and%20Channels/first-flow.html

[Mark Murphy]

import kotlinx.coroutines.*
import kotlinx.coroutines.flow.*

suspend fun doSomething(): String {
   val myFlow = flow { emit("hello") }
   return myFlow.first()
}

fun main() {
  GlobalScope.launch {
    println(doSomething())
  }
}

[voben]

How would I approach this if the flow isn’t guaranteed to emit only one item?

[Mark Murphy]

first() collects the first item only. So:

import kotlinx.coroutines.*
import kotlinx.coroutines.flow.*

suspend fun doSomething(): String {
   val myFlow = flow { emit("hello"); emit("world") }
   return myFlow.first()
}

fun main() {
  GlobalScope.launch {
    println(doSomething())
  }
}

still just prints hello, even though the flow emits two items.

[Mark Murphy]

see also https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.flow/first.html

[Seri]

You can also use Flow<T>.single() if you want to guarantee that only one value is published. https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.flow/single.html