Numba: Jitclass: support for __call__ etc

[oyamad]

Despite https://github.com/numba/numba/pull/1571#issuecomment-165205412, would it be possible for jitclass to support special methods such as

1. __call__
2. __getitem__, __setitem__
3. __repr__, __str__
4. __iter__

and others?

__call__ would be especially useful since it will allow the instance to look like a jitted function that can be passed to another jitted function as an argument. See also https://groups.google.com/a/continuum.io/forum/#!topic/numba-users/YE12tE2dIwY.

[datnamer]

Also multiple inheritance would be great. @sklam that probably deserves its own issue?

[moble]

@datnamer Multiple inheritance seems to work, at least from my simple first test. The only wrinkle is that I calling the super __init__ functions is a bit tricky, even for single inheritance (see #1694), but it seems to work. Is there a different problem that simple tests don't turn up?

[moble]

I would also add the operators __add__, __radd__, __mul__, etc.

[datnamer]

@moble ok thanks.

I was also thinking of ways for easy code reuse and lightweight abstractions- how about abstract base classes and or user defined protocols/magic methods? (similar to traits).

[j-towns]

I want to re-iterate that overloading of math operators like __add__, __mul__ etc is essential for Autograd to be compatible with Numba (which would be awesome).

How difficult would this be to implement? I'm happy to help if I can.

[sklam]

It gets really tricky to match the exact python semantic due to the __radd__ and reflection.

[AriKatz]

Does that mean JIT class support will stay as is? If not, what are the long term plans?

[sklam]

I have plans to expand the JIT class support. Few months ago, I was working on various jitclass features but I was slowed down by many tricky details. Some of these details, like the operating overloading, can be implemented but with great cost in code complexity. I think it is partially due to the technical debts in the internals of numba. So, I am taking a pause in pushing new features for jitclasses and trying to clean things up a bit.

[moble]

Is this closed by #1851, as suggested by one of the improvements listed in the release notes for version 0.26.0?

[moble]

I guess not, as my tests all fail. #1865 implies that special cases are needed, and that was closed in favor of (the still-open) #2187.

[aldanor]

Wondering if there's any plans on reviving this?

There's a few tricky magic methods, but would be very nice to at least have the 'easy' ones like __str__ / __repr__.

[andreapiso]

Another nice one to have would be __len__. Great to see __getitem__ and __setitem__ work tho!