C＃中没有参数类型的方法参数

Question

I try to use trial version of third party software written C#. While I try to use its API, I face up with a strange problem.

I am using visual studio 2015 and I found an interesting extended method signature in their API-SDK

  public static class CallExtendedInfoEx
  {
        public static void AddToSIPMessage(this CallExtendedInfo info,  msg);
  }

The second parameter type is not exist .Never seen before in C#. I try to give a generic Object parameter as second parameter, and C# Compiler gives a strange error

Severity Code Description Project File Line

Error CS1503 Argument 2: cannot convert from 'object' to '.'

It works with "null"...No compiler error or run time error [ ignored i think ]

How those guys can able to write such a code in C#? Is It Posssible? Any idea?

Note : I suspect from a code obscurification problem...But still i do not understand what is going here

  IL_0073:  call       void [CallExtendedInfoEx::AddToSIPMessage(class [VoIP.CallExtendedInfo,
                                                                                  class [VoIPSDK]''.'')

Answer 1

Well, looking at the ILDASM output, it's rather obvious that the argument has a perfectly valid type. Sure, it's a type that you can't actually name in C#, but it's perfectly valid in CLR at large.

The fact that you can pass null shouldn't be surprising - the argument is a reference type (or convertible from null ), so null is a perfectly valid value. On the other hand, expecting passing an object instance is entirely wrong - you can only pass more derived types as argument, not less . It's fine to pass string (more specific) instead of object (less specific), but not the other way around.

Most likely, this is either a method you shouldn't touch (ie not part of the public contract of the API/SDK), or you're expected to get instances of the argument from some other method - never using the explicit type anywhere.

Answer 2

This is not valid C# code. Some decompiler probably gave you that code, or the documentation where you copied this out of is faulty.