CODEWITHSUNDEEP
kotlinkotlin-coroutines
J.J. Beam
J.J. Beam

Reputation: 3059

Does Kotlin await in order in parameters?

Does Kotlin await exactly strictly in order

  1. recipient.await()
  2. msg.await()

at line 7:

 suspend fun sendEmail(r: String, msg: String): Boolean { //(6)
        delay(2000)
        println("Sent '$msg' to $r")
        return true
    }

    suspend fun getReceiverAddressFromDatabase(): String { //(4)
        delay(1000)
        return "[email protected]"
    }

    suspend fun sendEmailSuspending(): Boolean {
        val msg = async(CommonPool) {             //(3)
            delay(500)
            "The message content"
        }
        val recipient = async(CommonPool) {  //(5)
            getReceiverAddressFromDatabase()  
        } 
        println("Waiting for email data")
        val sendStatus = async(CommonPool) {
            sendEmail(recipient.await(), msg.await()) //(7)
        }
        return sendStatus.await() //(8)
    }

or in any order? I mean does Kotlin check first for recipient.await() and only after it completes go for check for msg.await()?

Upvotes: 1

Views: 225

Answers (1)

Marko Topolnik
Marko Topolnik

Reputation: 200168

Your question isn't await-specific and cuts much deeper, down to the evaluation order semantics of Kotlin itself.

So, here's a quote from the Kotlin language specification:

Function arguments are then evaluated in the order of their appearance in the function call left-to-right

Applied to your line of code:

sendEmail(recipient.await(), msg.await())

it is clear that first recipient.await() is evaluated and then msg.await(). The await() call doesn't complete until the Deferred in question has been completed.

Upvotes: 3

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