issue_comments: 661087703

Thanks @keewis. I did consider that but I assumed that kind of thing wouldn't be encouraged. Happy to go down that path, but I wonder if life would be easier if there were an extension API for this purpose.

I was thinking of something along these lines which would help keep things in check.

```python @xr.register_dataarray_as_method("cupy") class CupyAsMethod: def to_cupy(self): """Convert all data arrays to cupy."""

    for var in self.data_vars: 
        self.data_vars[var].data = cp.asarray(self.data_vars[var].data)

    return self

def to_numpy(self):
    """Convert all data arrays to numpy."""

    for var in self.data_vars: 
        self.data_vars[var].data = self.data_vars[var].data.get()

    return self

```

There would need to be some logic around dispatching as_numpy to CupyAsMethod.as_numpy, but only if the underlying data is cupy.

Perhaps some is_numpy, is_cupy boolean attributes would be useful?

I could go as you suggest and use the current accessor tooling to test this functionality out. Then upstream it into something more maintainable if it works out ok?