Is 'yield return' slower than “old school” return?

Question

I\'m doing some tests about yield return perfomance, and I found that it is slower than normal return.

I tested value variables (int, double, etc.) and some referenc

Answer 1

Because C# compiler converts iterator blocks (yield return) into state machine. State machine is very expensive in this case.

You can read more here: http://csharpindepth.com/articles/chapter6/iteratorblockimplementation.aspx