Question

I wrote a fairly complex method that yield-returns IEnumerable<string>, but when I inspected the compiler output in Reflector, I didn’t understand a specific part of the compiler-generated implementation of IEnumerator:

void IDisposable.Dispose() {     switch (this.<>1__state)     {         case 1:         case 2:         case 3:             switch (this.<>1__state) // empty switch! why?!             {             }             break;          default:             return;             try   // What?! AFTER return?!             {             }             finally // is the try-finally block anyhow relevant?             {                 this.<>m__Finallya();             }             break;     }     this.<>m__Finally7(); } 

I’m guessing (or hoping) that Reflector misplaced the closing brace of the outer switch, and that it should be directly after the return. Still, I don’t understand why there is an empty switch in case 3, or why m__Finallya is being called in a finally block. (Is there a semantic difference between running normally and inside a finally block? Other than CER’s, which I don’t have in my code.)

For reference, here is the IL:

.method private hidebysig newslot virtual final          instance void  System.IDisposable.Dispose() cil managed {   .override [mscorlib]System.IDisposable::Dispose   // Code size       69 (0x45)   .maxstack  2   .locals init ([0] int32 CS$0$0000,            [1] int32 CS$0$0001)   IL_0000:  ldarg.0   IL_0001:  ldfld      int32 FBD.TIP.Reader.MissingMessagesReader/'<GetMissingMessages>d__0'::'<>1__state'   IL_0006:  stloc.0   IL_0007:  ldloc.0   IL_0008:  ldc.i4.1   IL_0009:  sub   IL_000a:  switch     (                          IL_001c,                         IL_001c,                         IL_001c)   IL_001b:  ret   IL_001c:  ldarg.0   IL_001d:  ldfld      int32 FBD.TIP.Reader.MissingMessagesReader/'<GetMissingMessages>d__0'::'<>1__state'   IL_0022:  stloc.1   IL_0023:  ldloc.1   IL_0024:  ldc.i4.2   IL_0025:  sub   IL_0026:  switch     (                          IL_0035,                         IL_0035)   IL_0033:  br.s       IL_003e   .try   {     IL_0035:  leave.s    IL_003e   }  // end .try   finally   {     IL_0037:  ldarg.0     IL_0038:  call       instance void FBD.TIP.Reader.MissingMessagesReader/'<GetMissingMessages>d__0'::'<>m__Finallya'()     IL_003d:  endfinally   }  // end handler   IL_003e:  ldarg.0   IL_003f:  call       instance void FBD.TIP.Reader.MissingMessagesReader/'<GetMissingMessages>d__0'::'<>m__Finally7'()   IL_0044:  ret } // end of method '<GetMissingMessages>d__0'::System.IDisposable.Dispose 

Answer 1

That is simply reflector struggling to keep up with the IL that has been generated (since iterator blocks don’t have to relate to ‘normal’ C# as long as they are valid IL). In particular, the ret is after the finally block.