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After experimenting with an iterator block I noticed the generated IL code is not what I expect it to be. Instead of a try-finally block a try-fault block is generated, which I have never seen. I noticed that the compiler doesn't allow me use the fault keyword in 'handwritten' C#. Is there any difference between the 2? C# code: static IEnumerable<string> ReadAllLines(string fileName) { using (var file = System.IO.File.OpenText(fileName)) { string s; while ((s = file.ReadLine()) != null) { yield return s; } } } MSIL Code: .method private hidebysig newslot virtual final instance bool MoveNext() cil managed { .override [mscorlib]System.Collections.IEnumerator::MoveNext .maxstack 3 .locals init ( [0] bool CS$1$0000, [1] int32 CS$4$0001, [2] string CS$0$0002, [3] bool CS$4$0003) L_0000: ldarg.0 // try body L_008d: leave.s L_0097 L_008f: ldarg.0 L_0090: call instance void ConsoleApplication2.Program/<ReadAllLines>d__0::System.IDisposable.Dispose() L_0095: nop L_0096: endfinally L_0097: nop L_0098: ldloc.0 L_0099: ret .try L_0000 to L_008f fault handler L_008f to L_0097 } The interesting line is the last line of the IL where a fault handler is specified, where in a normal try-finally block a finally handler is specified.

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