Why does next statement after yield return get executed?

Question

I have the following function that iterates some rows and searches for files in a database. A null gets returned by the repository if file is not found in the database and the function should then return an empty ResultRow. The Assert() after the if statement fires in some cases. Why? How is that possible?

IEnumerable<ResultRow> DoRows(SequenceListWithQc list, 
IList<TestSpecification> testSpecs, bool writeResults=false)
{
    foreach (var row in list.Rows)
    {
        var result = new ResultRow();

        result.FileName = row.Columns[list.Headers.IndexOf("File Name")];

        var rawFile = repository.GetRawFileByFilename(result.FileName);

        if (rawFile == null)
        {
            yield return result;
        }

        Debug.Assert(rawFile != null);
    }
}

Immediately after the yield? It is also possible that we go for another loop and that in the next loop, rawFile is null... — willeM_ Van Onsem
– willeM_ Van Onsem, Commented May 24, 2017 at 13:01
Another issue I see is you are doing row.Columns[list.Headers.IndexOf("File Name")], if the file is not found, you have an index of -1 and thus an OutOfRangeException. — Guillaume Beauvois
– Guillaume Beauvois, Commented May 24, 2017 at 13:09

robaudas · Accepted Answer · 2017-05-24 13:15:03Z

2

You can call continue to move onto the next row in the loop

    if (rawFile == null)
    {
        yield return result;
        continue;
    }

answered May 24, 2017 at 13:15

robaudas

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