I was reading the documentation <https://kotlinlan...
# coroutines
j
I was reading the documentation https://kotlinlang.org/docs/reference/coroutines/select-expression.html, and when I tried to execute the code
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import kotlinx.coroutines.*
import kotlinx.coroutines.channels.*
import kotlinx.coroutines.selects.*

suspend fun selectAorB(a: ReceiveChannel<String>, b: ReceiveChannel<String>): String =
    select<String> {
        a.onReceiveOrNull { value -> 
            if (value == null) 
                "Channel 'a' is closed" 
            else 
                "a -> '$value'"
        }
        b.onReceiveOrNull { value -> 
            if (value == null) 
                "Channel 'b' is closed"
            else    
                "b -> '$value'"
        }
    }
    
fun main() = runBlocking<Unit> {
    val a = produce<String> {
        repeat(4) { send("Hello $it") }
    }
    val b = produce<String> {
        repeat(4) { send("World $it") }
    }
    repeat(8) { // print first eight results
        println(selectAorB(a, b))
    }
    coroutineContext.cancelChildren()        
}
The compiler gave warning that
onReceiveOrNull
was deprecated:
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'onReceiveOrNull: SelectClause1<E?>' is deprecated. Deprecated in favor of onReceiveOrClosed and onReceiveOrNull extension
I guess this is not yet applied in the guide from the documentation. May I ask how I should change the code?
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suspend fun selectAorB(a: ReceiveChannel<String>, b: ReceiveChannel<String>): String =
    select<String> {
        a.onReceiveOrClosed {  
            if (it.isClosed)
                "Channel 'a' is closed"
            else
                "a -> '${it.value}'"
        }
        b.onReceiveOrClosed { 
            if (it.isClosed)
                "Channel 'b' is closed"
            else
                "b -> '${it.value}'"
        }
    }
Would this be the preferred way for now?
t
If your channel contains only non-null values, go for
onReceiveOrNull
. There is an extension on
Channel<T : Any>
that is not deprecated, but rather hard to use (because the member function is picked first), you need to import the function with an alias If your channel contains nullable values you could use
onReceiveOrClosed
, but test thoroughly as this function returns an inline class (still an experimental language feature)
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