How CLR handles extern method calls in C#

Question

I want to ask why all extern method calls are static? How the CLR handles these calls?

Answer 1

Extern method calls are to unmanaged code. As such, it doesn't make sense to be called on a (managed) object instance - the first (hidden) argument in an instance method is the instance reference, aka this. Typically, extern methods just involve simple types (primitives, string, etc) - not objects (except perhaps arrays - and even they are often resolved to IntPtr first).