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copied!<p>The lamda version is actually not slower. I just did a quick test and the delegate version is about 30% faster.</p> <p>Here is the codez:</p> <pre><code>class Blah { public void DoStuff() { } } List<Blah> blahs = new List<Blah>(); DateTime start = DateTime.Now; for(int i = 0; i < 30000000; i++) { blahs.Add(new Blah()); } TimeSpan elapsed = (DateTime.Now - start); Console.WriteLine(string.Format(System.Globalization.CultureInfo.CurrentCulture, "Allocation - {0:00}:{1:00}:{2:00}.{3:000}", elapsed.Hours, elapsed.Minutes, elapsed.Seconds, elapsed.Milliseconds)); start = DateTime.Now; foreach(var bl in blahs) { bl.DoStuff(); } elapsed = (DateTime.Now - start); Console.WriteLine(string.Format(System.Globalization.CultureInfo.CurrentCulture, "foreach - {0:00}:{1:00}:{2:00}.{3:000}", elapsed.Hours, elapsed.Minutes, elapsed.Seconds, elapsed.Milliseconds)); start = DateTime.Now; blahs.ForEach(bl=>bl.DoStuff()); elapsed = (DateTime.Now - start); Console.WriteLine(string.Format(System.Globalization.CultureInfo.CurrentCulture, "lambda - {0:00}:{1:00}:{2:00}.{3:000}", elapsed.Hours, elapsed.Minutes, elapsed.Seconds, elapsed.Milliseconds)); </code></pre> <p>OK, So I've run more tests and here are the results.</p> <ol> <li><p>The order of the execution(forach, lambda or lambda, foreach) didn't make much difference, lambda version was still faster:</p> <pre>foreach - 00:00:00.561 lambda - 00:00:00.389 lambda - 00:00:00.317 foreach - 00:00:00.337</pre></li> <li><p>The difference in performance is a lot less for arrays of classes. Here are the numbers for Blah[30000000]:</p> <pre>lambda - 00:00:00.317 foreach - 00:00:00.337</pre></li> <li><p>Here is the same test but Blah being a struct:</p> <pre>Blah[] version lambda - 00:00:00.676 foreach - 00:00:00.437 List version: lambda - 00:00:00.461 foreach - 00:00:00.391</pre></li> <li><p>Optimized build, Blah is a struct using an array.</p> <pre>lambda - 00:00:00.426 foreach - 00:00:00.079</pre></li> </ol> <p><strong>Conclusion:</strong> There is no blanket answer for performance of foreach vs lambda. The answer is <em>It depends</em>. <a href="http://diditwith.net/2006/10/05/PerformanceOfForeachVsListForEach.aspx" rel="nofollow noreferrer">Here</a> is a more scientific test for <code>List<T></code>. As far as I can tell it's pretty damn efficient. If you are really concerned with performance use <code>for(int i...</code> loop. For iterating over a collection of a thousand customer records (example) it really doesn't matter all that much.</p> <p>As far as deciding between which version to use I would put potential performance hit for lambda version way at the bottom.</p> <p><strong>Conclusion #2</strong> <code>T[]</code> (where T is a value type) foreach loop is about 5 times faster for this test in an optimized build. That's the only significant difference between a Debug and Release build. So there you go, for arrays of value types use foreach, everything else - it doesn't matter.</p>

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