How to return a value inside a coroutine scope kotlin, android

private fun getUserIdByEmail(email: String): String {
    var userId = ""
    CoroutineScope(IO).launch {
        try {
            val querySnapshot = user3CollectionRef
                .whereEqualTo("userEmail", email)
                .get()
                .await()
            if (querySnapshot.documents.isNotEmpty()) {
                for (document in querySnapshot.documents) {
                    userId = document.id
                }
            } else {
                withContext(Dispatchers.Main) {
                    toast("No Match")
                }
            }

        } catch(e: Exception) {
            withContext(Dispatchers.Main) {
                toast(e.message.toString())
            }
        }

        Log.e("a7a", userId)
        withContext(Dispatchers.Default) {
            return userId
        }
    }
}

That’s the function I’m using to query through firebase documents, the thing is I want to return the userId which is a variable that I defined in the first line of the function, when I place the return block outside the coroutine scope, it returns an empty string, how do I return it inside the scope so it can run when the coroutine is finished, or any other way to return after the coroutine is finished

>Solution :

In order to make a function returns a pending value; it should be a suspend function to return the value asynchronously.

Then, instead of the launch builder, the async/await builder can be used to return a Deferredvalue.

await() waits until it’s assigned a value by the Coroutine

Applying that in code:

private suspend fun getUserIdByEmail(email: String): String {

   val userId = CoroutineScope(IO).async {
        
        var tempId = ""
        
        try {
            val querySnapshot = user3CollectionRef
                .whereEqualTo("userEmail", email)
                .get()
                .await()
            if (querySnapshot.documents.isNotEmpty()) {
                for (document in querySnapshot.documents) {
                    tempId = document.id
                }
            } else {
                withContext(Dispatchers.Main) {
                    toast("No Match")
                }
            }

        } catch(e: Exception) {
            withContext(Dispatchers.Main) {
                toast(e.message.toString())
            }
        }

        Log.e("a7a", tempId)
        withContext(Dispatchers.Default) {
            return@async tempId
        }
    }
    
    return userId.await() // waits until it's assigned a value from the Coroutine
}