Posted by: leppie | December 7, 2009

Calling an instance method in the CLR without an instance

A question came up how StackOverflow, blah.

I have heard about this behaviour being valid in C++, so I thought I would test it on the CLR.

.class Program
  .method static void  Main(string[] args)
    .locals init ([0] class Program p)
    ldloc.0 // but wait, it's still null!
    call   instance void Program::Awesome()

  .method instance void Awesome()
    ldstr      "Awesome!"
    call       void [mscorlib]System.Console::WriteLine(string)

  .method public specialname rtspecialname instance void  .ctor()
    call       instance void [mscorlib]System.Object::.ctor()

As you can see if you compile the program, “Awesome!” is printed.

Now run PEVerify. As you can see, perfect valid CLR code.

But how? And why wont in work in C#?

The C# compiler will in all cases (even weirdly, but probably for good reason) emit a callvirt instead of the call I used. This causes the runtime to perform a null check.

Secondly, the is no instance member access, so no references to ‘this’ need to be made.

Why is this like this? Not sure, but if I would guess, they left this specification loose, to allow for more flexibility in other languages.



  1. I guess these posts explains it –,,

    • Thanks for those links 🙂

      I did not really bother looking around 😦

  2. Hello,
    It has been a while since I have seen visible progress available for general public consumption. Will there be anymore work on this project (Ironscheme) this year (2010) ? Thank you. Good day.

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