Hey guys, I’m trying to understand `Job`’s

cancel

method. I’m working on creating a class that implements

CoroutineScope

and I’m following the example here https://github.com/Kotlin/kotlinx.coroutines/blob/master/core/kotlinx-coroutines-core/test/guide/example-context-10.kt. I would expect that

job.cancel()

would return true in this case since the invocation of cancel is what cancels the job, however, when I print the result of

job.cancel()

I get false.

fun destroy() {
     val temp = job.cancel()
     print(temp.toString()) //prints "false" even though I would expect it to print "true"
}

Am I misunderstanding cancel?

Documentation on cancel result is wrong. In fact

cancel

on

Job()

always returns

false

at them moment. It might change.

@elizarov Thanks for the clarification! Any thoughts on writing tests for coroutine cancelation scenarios?

We have tons of test, but they are all useless, since we don’t have any real use-cases for that boolean. It is just a left-over from earlier work. The proposal is to remove it: https://github.com/Kotlin/kotlinx.coroutines/issues/713

Thanks @elizarov for the information! The only (current) use we had for the boolean was in unit testing the coroutine to ensure that it was cancelled properly, but we'll figure out another way.