Prototype Promise class for discussion.

[alexchamberlain]

Simple Promise prototype, with basic get/set and exception handling.

Open questions include:

• Do we need separate _data and _exception members, or would testing for an exception be sufficient?
• Do we need a _done or is _data is not None or _exception is not None sufficient? I think we do so you can pass back None.

ToDo

• Add some documentation

Thoughts? Any other test cases needed?

[njsmith]

It looks like you're reimplementing curio.Event along the way here?

[alexchamberlain]

It is very similar, indeed. Do they serve the same purpose? If so, maybe it would be sufficient to add data/exception elements to Event.

[njsmith]

I don't think it makes sense to add data/exception elements to Event, but an Event could replace your done bool + condition variable. (You'd use the condition variable's locking, but it isn't doing anything here anyway, because you never hold the lock over a yield.)

[alexchamberlain]

Done; I've left it as 2 commits, but can squash before this is landed.