If I need a `coroutineScope { }` in a suspend func...

# arrow

[dave08]

If I need a coroutineScope { } in a suspend function, do I need to put the either { } outside or inside of it (does it matter)? Or maybe there's a variant of either { } that does that?

[simon.vergauwen]

They behave slightly different, and you should use whatever makes sense for your use-case.

If either is inside coroutineScope then it can never cancel the coroutineScope.

coroutineScope {
  either<String, Int> {
    launch { delay(1_000_000) }
    ensureNotNull(null) { "Fails" }
  } // Either.Left("Fails")
} // waits 1_000_000 completion

If you either is outside of coroutineScope it can cancel or short-circuit the coroutineScope.

either<String, Int> {
  coroutineScope {
    launch { delay(1_000_000) }
    ensureNotNull(null) { "Fails" }
  } // Finishes "immediately", and cancels delay
} // Either.Left("Fails")