Would you accept coroutine as app_factory?

Easy enough to do.

I'm not sure how that would work when running the code in production. Eg. Gunicorn doesn't accept a coroutine, and if you're using web.run_app(), you'd have to do something ugly with loop.run_until_complete.

Why would a coroutine be useful? surely anything requiring a running loop can be done in startup coroutines?

Perhaps having app_factory as a coroutine could encourage people to setup their app in a way which will be hard to deploy?

Very happy to add the functionality if it's useful.

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Merging #96 into master will increase coverage by 0.03%.
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  Branches       92      92              
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Well, let's discuss.
My main motivation is creating every async object (the object that should cooperate with asyncio loop) inside a coroutine.
It allows to skip explicit event loop passing but get implicit running loop used for coro execution.
Maybe we end up with something like run_forever() from python/asyncio#465
I still don't know how to better integrate this approach with gunicorn.
We could add support for coroutine factory to aiohttp.worker easy though.
And after that got smoothly to dropping ._init_loop() trick at all.

Let's leave the coroutine question for now. Happy to add it later if it's needed.