convert PyUntypedArray to Bound API

[Icxolu]

Following #410

This migrates PyUntypedArray to the Bound API. This introduces PyUntypedArrayMethods to implement the methods on Bound<PyUntypedArray>. Additionally this also implements the trait on Bound<PyArray<T, D>>, via as_untyped, because we will not be able to provide a Deref implementation anymore, due to orphan rules and the deref to Bound<PyAny>. This seemed like the most reasonably option to keep the same ergonomics.

[davidhewitt]

we will not be able to provide a Deref implementation anymore, due to orphan rules and the deref to Bound. This seemed like the most reasonably option to keep the same ergonomics.

Should we be changing the PyO3 deref implementation to make it possible for downstream to decide the target type? This might be relevant in class hierarchies, for example.

Alternatively we could experiment with removing the deref-to-pyany blanket and instead implement PyAnyMethods for all types Bound<T>.

[davidhewitt]

Alternatively we could experiment with removing the deref-to-pyany blanket and instead implement PyAnyMethods for all types Bound.

I guess the problem with doing that is that things like list.iter() become ambiguous between the two traits, so the answer is that that approach doesn't work.

[Icxolu]

Should we be changing the PyO3 deref implementation to make it possible for downstream to decide the target type? This might be relevant in class hierarchies, for example.

It might be a good idea experimenting with that. I don't think it would be a huge deal here, nice to have, but not a deal breaker either. Maybe we can add an associated type to DerefToPyAny, which defaults to PyAny? For class hierarchies this would probably involve pyo3s macro code.

[davidhewitt]

So, given that the deref idea doesn't work out, I guess that the design as proposed here is the right way to proceed?

[adamreichold]

So, given that the deref idea doesn't work out, I guess that the design as proposed here is the right way to proceed?

Yes, I just did not find time to complete the review here yet.

[davidhewitt]

No problem, I have also had a disrupted week. I'm hoping to go through the list of actions for 0.21 and see what remains before the final release later.