http://blogs.msdn.com/matt/archive/tags/WHAT_2100_/default.aspxTags: WHAT!en-USCommunityServer 2.1 SP1 (Build: 61025.2)http://blogs.msdn.com/matt/archive/2008/07/22/foreach-is-duck-typed.aspxTue, 22 Jul 2008 20:04:00 GMT91d46819-8472-40ad-a661-2c78acb4018c:8764433MattManela5http://blogs.msdn.com/matt/comments/8764433.aspxhttp://blogs.msdn.com/matt/commentrss.aspx?PostID=8764433<P>I thought I know how the foreach construct worked under the covers. I figured the compiler would check if the type being iterated over implement IEnumerable or IEnumerator.&nbsp; And if so it will call MoveNext and Current to loop over the elements.&nbsp; But then I read this:</P> <P><A title=http://blogs.msdn.com/kcwalina/archive/2007/07/18/DuckNotation.aspx href="http://blogs.msdn.com/kcwalina/archive/2007/07/18/DuckNotation.aspx" mce_href="http://blogs.msdn.com/kcwalina/archive/2007/07/18/DuckNotation.aspx">http://blogs.msdn.com/kcwalina/archive/2007/07/18/DuckNotation.aspx</A></P> <P>In that post Krzysztof reveals that in reality implementation of those interfaces are NOT checked.&nbsp; In fact, it uses duck typing to determine if iteration can occur.&nbsp; The compiler will just look for a method that matches a certain signature and use that.&nbsp; </P> <P>Very interesting!</P><img src="http://blogs.msdn.com/aggbug.aspx?PostID=8764433" width="1" height="1">C#ProgrammingWHAT!