Problem description

Currently, it appears that "dimension"/"coordinate" labels must be strings. However, in more rigorous software engineering applications it is often desirable to use something more organized/structured for labels, e.g. enums. I think it would be great if xarray supported this.

Obviously storing to e.g. NetCDF necessitates string-valued field names, so I would think calling str could be appropriate when performing this sort of serialization. This is what pandas seems to do (see below). But I imagine there might be other issues that would need to be resolved to do what I'm suggesting...?

Code sample

import enum

import numpy as np
import pandas as pd
import xarray as xr

class CoordId(enum.Enum):
    LAT = 'lat'
    LON = 'lon'

pd.DataFrame({CoordId.LAT: [1,2,3]}).to_csv()
# Returns: ',CoordId.LAT\n0,1\n1,2\n2,3\n'

xr.DataArray(
    data=np.arange(3 * 2).reshape(3, 2),
    coords={CoordId.LAT: [1, 2, 3], CoordId.LON: [7, 8]},
    dims=[CoordId.LAT, CoordId.LON],
)
# Fails: TypeError: dimension CoordId.LAT is not a string

Output of xr.show_versions()