Lots of API functions use structures, and a lot of structures have size member.
So when we try to decompile following code we will end up with error.
And we decompile with Telerik Decompiler we get:
you can see that line
size = Marshal.SizeOf(instance),can't be compiled since "instance" object is not yet created (== unassigned, non existing, and compiler raises error CS0165).