__methodptr in decompiled C# code

Question

I'm using dotPeek to dive deeper into the C# compiler magic, and something in decompiled code caught my attention. I'm creating an Action<int> instance and pass it to Start() method, the compiler generates the following:

new Program().Start(new Action<int>((object) cDisplayClass1, __methodptr(<Main>b__0)));

I generally understand what's happening here, my only question is what is __methodptr? To be exact, where does it come from? Is it from IL? dotPeek doesn't know a thing about it or the assembly containing it. Google doesn't give a precise answer either, only the same snippets of code with no explanations whatsoever.

Thank you!

Answer 1

the __methodptr corresponds to IL instruction ldftn , roughly speaking ldftn load "function pointer" onto evaluation stack. here is a sample:

the de-compiled source:

   private static void Main(string[] args)
    {
      Program.\u003C\u003Ec__DisplayClass0_0 cDisplayClass00 = new Program.\u003C\u003Ec__DisplayClass0_0();
      cDisplayClass00.xx = 100;
      // ISSUE: method pointer
      new Action((object) cDisplayClass00, __methodptr(\u003CMain\u003Eb__0))();
      Console.WriteLine(cDisplayClass00.xx);
    }

the IL:

1 load function pointer class::method

IL_000f: ldloc.0      // cDisplayClass00
IL_0010: ldftn        instance void TestIL.Program/'<>c__DisplayClass0_0'::'<Main>b__0'()

2 new a delegate passing object and function pointer

IL_0016: newobj       instance void [mscorlib]System.Action::.ctor(object, native int)
IL_001b: stloc.1      // V_1

3 call the delegate

IL_001c: ldloc.1      // V_1
IL_001d: callvirt     instance void [mscorlib]System.Action::Invoke()
IL_0022: nop 

Answer 2

You should replace code as follows :

new Action(cDisplayClass00.Mainb__0))();

So to speak, function pointer to auto generated method on auto generated class.