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DaedTech[^]:

I ran across a method that returned an IEnumerable<t> recently, and I implicitly typed its return value. During the course of a series of method extractions, code movement, and general refactoring, I wound up with some code that passed the various unit tests in place but failed curiously at runtime. After peering at it for a few minutes and going through once in the debugger, I traced it to a problem that you don’t see every day, and one that probably would have had me tearing my hair out if I didn’t have a good working understanding of what the “yield” keyword in C# does. So today, I’ll present the essence of this problem in the hopes that, if you weren’t aware of it, you are now.