Making asynchronicity explicit

In Kotlin, managing asynchronous operations is streamlined with coroutines. However, the asynchronous nature of a function is not always apparent from its name or signature, which can lead to misunderstandings about its behavior.

Consider a simple asynchronous function defined within a CoroutineScope:

fun CoroutineScope.getResult() = async {
    delay(100)
    "OK"
}

Since this function implicitly returns a Deferred object, not the direct result, the following code might not behave as expected:

println("Result: ${getResult()}")

This prints a reference to the Deferred object instead of OK:

> Result: DeferredCoroutine{Active}@...

If you’ve been following along with the book, you will already know that to obtain the actual result, the await() function must be used:

println("Result: ${getResultAsync().await()}")

This code correctly waits for Deferred to complete and then prints...