Add helper that automatically gets services according to type hints?

[hynek]

As it just came up in #86, I use a pattern similar to this all the time:

class Inner:
    ...

@dataclass
class Wrapper:
    foo: Inner

registry.register_factory(Inner, Inner)
registry.register_factory(Wrapper, lambda svcs_container: Wrapper(svcs_container.get(Inner)))

svcs will always be non-magical by default, but I guess nothing speaks against adding a helper that makes the lambda superfluous by looking at the type hints of the factory and calling svcs_container.(a)get on the required types automatically:

registry.register_factory(Inner, Inner)
registry.register_factory(Wrapper, svcs.inspect_and_get(Wrapper))

Since this would only be a helper, it wouldn't also have the pressure to implement all edge cases because the escape hatch of just writing your own lambda is always there.

[pauleveritt]

FWIW I have a registry project with the kind of injection you describe. It’s critical for a larger effort I have in mind.

I’m investigating re-homing my stuff atop svcs… going through a gap analysis now to see which of my darlings (features) to kill.

[proofit404]

To my understanding we have a couple of corner cases here:

1. Please, please, please, do not call it inspect_and_get
2. We need to have sync and async versions of same function
3. handle keyword arguments defaults

   class Srvc:
       a: DepA
       b: DepB = DepB()

   This would be correct case if registry defines only DepA.
4. Passed class could be without type annotations

One benefit I see for factory builder over registry method is ability to customize factory:

fctr = make_factory(Srvc)

def factory(svcs_container):
    with fctr(svcs_container) as instance:
        yield instance

registry.register(Srvc, factory)

In case our service has it's own life circle an supposed to be used as context manager.

[proofit404]

@hynek let me put it this way 🌴 🍸