arbitrary_self_types approaching stabilisation, interaction with PyAnyMethods etc

[davidhewitt]

We built the PyAnyMethods traits with the assumption that we might be able to use arbitrary_self_types as an off-ramp in the future. The traits seem to have been adopted well though it would be nice to remove them again for simplicity if possible.

The latest iteration of arbitrary_self_types is now feature complete on nightly and looks like there might be a stabilisation report soon: rust-lang/rust#44874 (comment)

Has anyone got some time / energy to experiment with this for our potential use in PyO3? As well as in PyAnyMethods, it might be useful in PyRef<MyClass> / Bound<MyClass> etc. for #[pymethods] receivers.

I would love to try, but I am experiencing a drought of time which is probably lasting until March 😢

cc @adetaylor

[adetaylor]

David's previous thoughts here

[LilyFoote]

I'll take a look at this.