Nick Coghlan wrote:
The main primitive I personally want out of an async API is a task-based equivalent to concurrent.futures.as_completed() . This is what I meant about iteration being a bit of a mess: the way the as_completed() works, the suspend/resume channel of the iterator protocol is being used to pass completed future objects back to the calling iterator. That means that channel *can't* be used to talk between the coroutine and the scheduler,
I had to read this a couple of times before I figured out what you're talking about, but I get it now.
This is an instance of a general problem that was noticed back when I was discussing my cofunctions idea: using generator-based coroutines, it's not possible to have a "suspendable iterator", because that would require "yield" to have two conflicting meanings: "suspend this coroutine" on one hand, and "provide a value to my caller" on the other.
Unfortunately, I suspect that a truly elegant solution to this problem will require yet another language addition -- something like
yield for item in subtask(): ...
which would run a slightly different version of the iterator protocol in which values to be yield are wrapped somehow (I haven't figured out all the details yet).