[nullwasamistake]

I understand why you didn't, but async brings a whole new opportunity to try! At least in library form.

Fibers are great because you can pretend they're threads. Everyone knows threads. Async is a legit PITA even if you're familiar with it. And the local state stored for a fake thread is often useful. When doing async I find myself frequently building hacky hashmaps to hold local variables values. websocket code is a good example of worse-case. 20k ongoing connections held by async (1 thread per core). It's a nightmare in everything except Vert.X Sync (fibers in Java) or maybe Golang and Erlang.

With fibers you get to keep all your local variables and "pretend" threads actually exist. It's a huge boon for productivity in the few languages where it's possible