Yielding to enumeration in C#

I just discovered the yield keyword and I can’t believe I hadn’t found it sooner. I became a huge fan of using LINQ from the moment I started using it and I am in the habit of passing and returning IEnumerable whenever possible.

Recently I had a problem where I was reading the lines of a CSV file using this code:

var csvdata = File.ReadAllLines(filename);

That seemed to work fine, but for some mysterious reason (that I still am uncertain of) it had problems reading the CSV file cleanly from a networked drive for some users. I have no idea why but I wanted to use something a bit more transparent.

A bit of googling turned up a solution that used a keyword I had never seen before:

private static IEnumerable<string> ReadLines(string path)
  using (StreamReader reader = new StreamReader(new FileStream(path, FileMode.Open)))
    string line;
    while ((line = reader.ReadLine()) != null)
      yield return line;

I marveled at this yield keyword, it allows a method to return a result as IEnumerable, with delayed evaluation (each item in the result set is only returned when it is asked for) without having to implement a new IEnumerable class.

Anyways, nothing ground breaking, but a pretty handy tool nonetheless. Its been a while since I posted anything and I figured this was as good as anything else I’ve been thinking of posting, but nice and simple.

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