Are you certain you want to expose this function to the script? A C++ function pointer is not compatible with the script function pointers. How do you plan for the script to obtain the C++ function pointer to pass to the operator() method in the first place?

Anyway, if you really do want to expose it, I suppose you could do something like this:

// First register a type to represent the C++ function pointer
engine->RegisterObjectType("cfunc", sizeof(void (*)()), asOBJ_VALUE | asOBJ_POD | asOBJ_PRIMITIVE); 
 
// Register the operator() as an opCall method receiving the cfunc type by value
engine->RegisterObjectMethod("MyObj", "MyObj &opCall(cfunc)", asMETHOD(Object, operator(), (void(&func)()), Object&), asCALL_THISCALL);

In the above I'm registering the cfunc as a POD type, but if you really want to expose this method to the script you should probably register it as a non-POD and provide appropriate constructors and assignment operators to guarantee that the function pointer is always valid. Otherwise the script might call the opCall() method with an invalid function pointer and your application will crash (or it might be exploited by malicious users to hack the computer).

Then you want to do the following:

engine->RegisterFuncdef("void CALLBACK()");
engine->RegisterObjectMethod("MyObj", "void opCall(CALLBACK@)", asMETHOD(Object, operator(), (asIScriptFunction*), void), asCALL_THISCALL);

Take a look at this article in the manual for more details.

Regards,

Andreas