[Numpy-discussion] Should unique types of all arguments be passed on in __array_function__?

[Marten van Kerkwijk]

More specifically:

Should we change this? It is quite trivially done, but perhaps I am missing
>> a reason for omitting the non-override types.
>>
>
> Realistically, without these other changes in NumPy, how would this
> improve code using __array_function__? From a general purpose dispatching
> perspective, are there cases where you'd want to return NotImplemented
> based on types that don't implement __array_function__?
>

I think, yes, that would be the closest analogy to the python operators.
Saves you from having separate cases for types that have and do not have
`__array_function__`.


> I guess this might help if your alternative array class is super-explicit,
> and doesn't automatically call `asmyarray()` on each argument. You could
> rely on __array_function__ to return NotImplement (and thus raise
> TypeError) rather than type checking in every function you write for your
> alternative arrays.
>

Indeed.


> One minor downside would speed: now __array_function__ implementations
> need to check a longer list of types.
>

That's true.

>
> Another minor downside: if users follow the example of
> NDArrayOperatorsMixin docstring, they would now need to explicitly list all
> of the scalar types (without __array_function__) that they support,
> including builtin types like int and type(None). I suppose this ties into
> our recommended best practices for doing type checking in
> __array_ufunc__/__array_function__ implementations, which should probably
> be updated regardless:
> https://github.com/numpy/numpy/issues/12258#issuecomment-432858949
>
>
Also true. It makes me wonder again whether passing on the types is useful
at all... But I end up thinking that it is not up to an implementation to
raise TypeError - it should just return NotImplemented.

If we'd wanted to give more information, we might also consider passing on
`overloaded_args` - then perhaps one has the best of both worlds.

All the best,

Marten
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