API: `asarray` API for `copy=...` kwarg

There was a plan to update NumPy’s asarray’s copy kwarg, however, this would mismatch with the array one. NumPy was currently aiming for possibly having an enum or maybe copy="never", but not a False/True/None flags.

I am a bit unclear about the desired API right now, since on NumPy it was explicitly argued against the True/False/None choice.

@charris has also brought up the idea to add a “please do not copy this array” flag to the array object itself to prevent accidental copy of large arrays.

[shoyer]

Yes, I was advocating for enums last time 🤦

I commented on the mailing list discussion advocating for True/False/None.

[shoyer]

I think 3-way True/False/None is a totally reasonable solution if we are designing this API from scratch.

The problem is that right now copy=False means “copy if needed” for NumPy, which is not what we would want copy=False to mean in the array API.

If we want to change what copy=False means, we’ll need a deprecation cycle in NumPy. That would be somewhat distruptive, but on the whole, it might be a good thing – it would turn up lots of cases where users are probably mistaken about what copy=False means. Also this would a relatively smooth deprecation, because there’s an easy backwards compatible work-around (just set copy=None instead) and we would not be changing the behavior of existing code beyond starting to raise an error message in some cases.