html_url,issue_url,id,node_id,user,created_at,updated_at,author_association,body,reactions,performed_via_github_app,issue
https://github.com/pydata/xarray/pull/5397#issuecomment-851618811,https://api.github.com/repos/pydata/xarray/issues/5397,851618811,MDEyOklzc3VlQ29tbWVudDg1MTYxODgxMQ==,37740986,2021-05-31T17:59:46Z,2021-05-31T17:59:46Z,CONTRIBUTOR,"Will it not cripple performance due to the non-lazy evaluation of the list ?

I also started the test for the concat function, I discovered that if the first element determine between `_dataarray_concat` and `_dataset_concat`. I am not sure if I need to do several commits (type checking dataset, type checking data array) and several test.

Here is the draft for the tests:
```
def test_concat_check_input_type():
    ds = Dataset({""foo"": 1}, {""bar"": 2})
    da = Dataset({""foo"": 3}, {""bar"": 4}).to_array(dim='foo')

    # concatenate a list of non-homogeneous types must raise TypeError
    with pytest.raises(TypeError, match=""Some elements in the input list datasets are not 'DataSet'""):
        concat([ds, da], dim=""foo"")

    # concatenate a list of non-homogeneous types must raise TypeError
    with pytest.raises(TypeError, match=""Some elements in the input list datasets are not 'DataArray'""):
        concat([da, ds], dim=""foo"")
```

Code I plan to add also for the typing check in `_dataarray_concat`:
```
    from .dataarray import DataArray
    arrays = list(arrays)
    if not all(isinstance(array, DataArray) for array in list(arrays)):
        raise TypeError(""Some elements in the input list datasets are not 'DataArray'"")
```
(I need to add `from .dataarray import DataArray` to be able to use the type)
","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,905848466
https://github.com/pydata/xarray/pull/5397#issuecomment-850666780,https://api.github.com/repos/pydata/xarray/issues/5397,850666780,MDEyOklzc3VlQ29tbWVudDg1MDY2Njc4MA==,37740986,2021-05-28T20:58:53Z,2021-05-28T20:58:53Z,CONTRIBUTOR,"Ok! I'll do that in the next few days :)
I'm trying to get more familiar with the whole procedure","{""total_count"": 0, ""+1"": 0, ""-1"": 0, ""laugh"": 0, ""hooray"": 0, ""confused"": 0, ""heart"": 0, ""rocket"": 0, ""eyes"": 0}",,905848466