Support instance-based activities

[jbbarth]

This has been discussed a little in #70 , but I open a separate issue for this. We'd like to be able to pass an object instance to Workflow.submit() directly to ease its instrumentation:

self.submit(Foo(bar))

The recent refactoring around activity tasks could help with that.

For now I have something working here: https://github.com/botify-labs/simpleflow/tree/feature/instance-based-activities but I'm not really satisfied (one more class concept, hacky generation of an Activity, "callable" still used everywhere where in fact we have an object, no automatic args/kwargs resolution, etc.). Will try to improve that later.

[ybastide]

[Speculating] Could we use metaclass thingies to defer the call to __init__ or wrap somewhat the future arguments?

[jbbarth]

I don't know "metaclass thingies" (yet), pointer?

[ybastide]

Sorry, no pointer found... __metaclass__, __new__, __call__ or some such things, but it's hand waving...

[jbbarth]

Oh ok, I thought there was something special in abc or equivalent to do lazy evaluation or some other black magic. I'll read the docs about metaclasses then!

[ybastide]

No magic, just metaprogramming :-)

It's easy, really. Just parse __init__'s arguments. If any is a Future, replace it with its result getter 😉

(I discovered a really marvelous implementation that this comment box's margin is too small to contain)

[ampelmann]

@ybastide gist it ? :)

[jbbarth]

Thanks Mr Fermat ;-) Actually I may find a smart solution with __new__, didn't know you have access to that in python!

[jbbarth]

Arg, last problem (but not least): examples work well with ONE instance of a given task, but they'll mix up in the registry if there are two of them. We need to refine their name to include a unique ID per object. Going down the rabbit hole :(