issue_comments: 335279657

@fujiisoup Thanks again for all your hard work on this and for my slow response. I've made another PR with tweaks to your logic for conflicting coordinates: https://github.com/fujiisoup/xarray/pull/5

Mostly, my PR is about simplifying the logic by removing the special case work arounds you added that check object identity (things like this_arr is self._variables[k] and v.variable is cv.variable). My concern is that nothing else in xarray relies on these types of identity checks, so adding these additional rules will make the logic harder to understand and rely on programmatically. If we try to make behavior "intuitive" for 80% of use-cases, it only makes the remaining 20% more baffling and error prone. This is the similar to the problem with dimension re-ordering and NumPy's mixed integer/slice indexing. So I would rather these leave out for now at the cost of making the API slightly more cumbersome. As I think we discussed previously, it is easier to relax error conditions in the future than to add new errors.