Understanding behavior of member functions loaded at runtime

[Maeriden via Digitalmars-d-learn]

============================================================
module dll;

struct S
{
	int a;
	int b;
	
	int method()
	{
		return a + b;
	}
}

============================================================

module test;

import core.sys.posix.dlfcn;
import core.stdc.stdio;
import dll;
pragma(lib, "dl");

pragma(mangle, S.method.mangleof)
__gshared int function(S* self) paramMethod;

__gshared int function()        noparamMethod;

void main(string[] args)
{
	void* lib = dlopen("dll.so", RTLD_LAZY);
	
	string funcName = S.method.mangleof;
	noparamMethod = cast(typeof(noparamMethod)) dlsym(lib, 
funcName.ptr);
	paramMethod   = cast(typeof(paramMethod))   dlsym(lib, 
funcName.ptr);
	
	
	int result = noparamMethod();
	printf("%d\n", result);
	
	S s = { 1, 1 };
	result = paramMethod(&s);
	printf("%d\n", result);
	
	result = s.method(); // Symbol resolved because of pragma(mangle)
	printf("%d\n", result);
	
	// Error: function dll.S.method () is not callable using 
argument types (S*)
	//result = S.method(&s);
	//printf("%d\n", result);
}

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dmd -fPIC -shared -defaultlib=libphobos2.so dll.d
dmd -defaultlib=libphobos2.so -L-rpath=. test.d


the output is
0
2
Segmentation fault

My questions are
1) Why does 'noparamMethod" return 0?
I assume that 'this' points to S.init but how does it know where 
to find it? What's going on?

2) typeof(S.method) is "int()". Why's that? In C++ it would have 
been "int(S* const)" and I though in D it would have been 
"int(S*)"
2.1) Is this related to why case 4 doesn't compile?

3) Why does case 3 crash? I assume it's because there is no 
argument so 'this' is null, but wouldn't the call be translated 
to "S.method(&s)"?