Does anyone know the difference between using `res...

# coroutines

[谢朋刚]

Does anyone know the difference between using resumeWithException and directly throwing an Exception within a suspend function?

[Youssef Shoaib [MOD]]

You mean like if you resume with something that immediately results in an exception? It's identical!

[谢朋刚]

If writes a suspend funciton using suspendCoroutine, you can use resumeWithException to throw an Exception

@SinceKotlin("1.3")
@InlineOnly
public inline fun <T> Continuation<T>.resumeWithException(exception: Throwable): Unit =
    resumeWith(Result.failure(exception))

[谢朋刚]

but we also can throwing an Exception directly.

[谢朋刚]

What is the difference?

[Youssef Shoaib [MOD]]

Both are identical in this case. `suspendCoroutine`'s block, if it raises an error, will be propagated as if you called resumeWithException.
However, you won't go through the dispatcher for instance, so actually throwing directly is ever so slightly more performant, while resumeWithException might allocate some objects

[谢朋刚]

Under what circumstances would these two behaviors differ?

[Zach Klippenstein (he/him) [MOD]]

The behavior should be the same in every case, I think. Why do you ask? Are you seeing something unexpected?

[谢朋刚]

I'm just wondering, what was the intention behind Kotlin's design of this function?

[Dmitry Khalanskiy [JB]]

The intention is to allow other parts of the system to make this function throw an exception, after the suspend function has already suspended. You are right that there really isn't much sense in suspending if you already know you already know you're going to throw an exception.

Please see the code snippet in the documentation https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines/suspend-cancellable-coroutine.html for a typical usage example of resumeWithException!