I have a code like this: ```launch { try { ...

# coroutines

[dimsuz]

I have a code like this:

launch {
  try {
    myCoroutine() // throws exception when executed
  } catch (e: Exception) {
    println("caught $e")
  }
}

and instead of catching it crashes. But if I replace try/catch with

runCatching { myCoroutine() }.exceptionOrNull()?.let { println("caught $e") }

it catches and prints exception.

Now, myCoroutine above involves calling android-related Retrofit library which has it's own coroutine adapters, so it might be doing some smarty stuff (debugger shows that continuation.resumeWithException() is called, maybe on different dispatcher), but I want to understand in general the difference between try/catch and `runCatching`: why can this situation happen and when I should use which approach to handling exceptions?

[octylFractal]

are you sure it's not throwing a Throwable instead of Exception?

[octylFractal]

runCatching is literally a try-`catch`:

public inline fun <R> runCatching(block: () -> R): Result<R> {
    return try {
        Result.success(block())
    } catch (e: Throwable) {
        Result.failure(e)
    }
}

[dimsuz]

hahaha, omg, that's it! I twisted my head in so many ways trying to understand what the hell happens here 🙂

[dimsuz]

whew, that's good that it turned out to be so stupid. I was afraid that runCatching somehow possesses some magic ways to do a proper catching. Never thought of checking its source, perhaps it would make me doubt that )

[Marcelo Hernandez]

Just be mindful that when Coroutines get cancelled, a CancellationException gets thrown. However it will not cause a crash. If you catch Throwable be sure to re-throw it if it is an instance of CancellationException so that the Coroutine cancels correctly. Otherwise you'll be treating the cancellation as is it were an actual error.

[Marcelo Hernandez]

More on this here https://kotlinlang.slack.com/archives/C1CFAFJSK/p1562606190132400?thread_ts=1562606190.132400&cid=C1CFAFJSK

[dimsuz]

Thank you!

[Marcelo Hernandez]

You're welcome 🙂