29 lines
873 B
Nim
29 lines
873 B
Nim
|
## The peculiarities of `discard` in `async` procedures
|
||
|
|
import chronos
|
||
|
|
|
||
|
|
proc failingOperation() {.async.} =
|
||
|
|
echo "Raising!"
|
||
|
|
raise (ref ValueError)(msg: "My error")
|
||
|
|
|
||
|
|
proc myApp() {.async.} =
|
||
|
|
# This style of discard causes the `ValueError` to be discarded, hiding the
|
||
|
|
# failure of the operation - avoid!
|
||
|
|
discard failingOperation()
|
||
|
|
|
||
|
|
proc runAsTask(fut: Future[void]): Future[void] {.async: (raises: []).} =
|
||
|
|
# runAsTask uses `raises: []` to ensure at compile-time that no exceptions
|
||
|
|
# escape it!
|
||
|
|
try:
|
||
|
|
await fut
|
||
|
|
except CatchableError as exc:
|
||
|
|
echo "The task failed! ", exc.msg
|
||
|
|
|
||
|
|
# asyncSpawn ensures that errors don't leak unnoticed from tasks without
|
||
|
|
# blocking:
|
||
|
|
asyncSpawn runAsTask(failingOperation())
|
||
|
|
|
||
|
|
# If we didn't catch the exception with `runAsTask`, the program will crash:
|
||
|
|
asyncSpawn failingOperation()
|
||
|
|
|
||
|
|
waitFor myApp()
|