How do I get funcref-like functionality to work within a_star.cpp?

[KnightNine]

I am working on Astar optimization and I want to try testing for straight paths before using astar when traversing octants/chunks of my hierarchal pathfinding loop. Since Godot's Astar algorithm is generic and isn't aware of any grid, it cannot assume straight paths, so I need to pass a user made function into the Astar object from GDscript to be used in the Astar algorithm. This function would take 2 point ids and return a PoolIntArray of point ids that is the path between the two points.

I've tried to copy code from func_ref.cpp to do this but cannot compile due to build errors. and I also have other questions about what I'm doing in the commentation.
here are the relevant functions:

//returns false if fail
bool AStar::set_straight_line_function(Object* p_obj, StringName &draw_straight_line_f_name) {

	ERR_FAIL_NULL_V(p_obj,false);

	//how do i check if StringName is empty?, will this work?
	ERR_FAIL_COND_V_MSG(draw_straight_line_f_name == "", false, "No defined Straight Line Function");

	//can i pass a StringName into vformat()? if not how do i extract the string from the StringName?
	ERR_FAIL_COND_V_MSG(p_obj->has_method(draw_straight_line_f_name), false, vformat("function %s does not exist within object",draw_straight_line_f_name));

	
	ObjectID id = p_obj->get_instance_id();
	//this check might be redundant
	ERR_FAIL_COND_V(id == 0, false);

	//test the function to ensure it works properly and returns the correct var type:

	// am i able to append ints to this array even though they're not Variants?
	Array p_args;
	p_args.append(0);
	p_args.append(1);

	//how do I check the number of parameters of the straight_line_function is 2?
	Variant result = p_obj->callv(draw_straight_line_f_name, p_args);
	//unsure if this will work:
	/*
	- `result.get_type() != 21` does this make sense?
	- can i pass a StringName into vformat()? if not how do i extract the string from the StringName?
	*/
	ERR_FAIL_COND_V_MSG(result.get_type() != 21, false, vformat("straight line function %s, does not return a PoolIntArray", draw_straight_line_f_name));


	straight_line_function = draw_straight_line_f_name;
	function_source_id = id;
	return true;
}

PoolIntArray AStar::_get_straight_line(int from_point, int to_point) {
	int from = from_point;
	int to = to_point;

	

	
	ERR_FAIL_COND_V(function_source_id == 0, PoolIntArray());

	Object* obj = ObjectDB::get_instance(function_source_id);

	ERR_FAIL_COND_V(!obj, PoolIntArray());

	// am i able to append ints to this array even though they're not Variants?
	Array p_args;
	p_args.append(from_point);
	p_args.append(to_point);

	Variant result = obj->callv(straight_line_function, p_args);

	//can i just return the result even though it is a Variant?
	return result;

}

and I'm getting these errors when trying to build:

C:\Users\Alex\Desktop\Godot_v3.1.1-stable_mono_win64\godot master\godot\core\method_bind.gen.inc(1784): error C2039: 'convert': is not a member of 'PtrToArg<P2>'
        with
        [
            P2=StringName &
        ]
C:\Users\Alex\Desktop\Godot_v3.1.1-stable_mono_win64\godot master\godot\core\method_bind.gen.inc(1784): note: see declaration of 'PtrToArg<P2>'
        with
        [
            P2=StringName &
        ]
C:\Users\Alex\Desktop\Godot_v3.1.1-stable_mono_win64\godot master\godot\core\method_bind.gen.inc(1781): note: while compiling class template member function 'void MethodBind2R<T,R,P1,P2>::ptrcall(Object *,const void **,void *)'
        with
        [
            T=AStar,
            R=bool,
            P1=Object *,
            P2=StringName &
        ]
C:\Users\Alex\Desktop\Godot_v3.1.1-stable_mono_win64\godot master\godot\core\method_bind.gen.inc(1800): note: see reference to class template instantiation 'MethodBind2R<T,R,P1,P2>' being compiled
        with
        [
            T=AStar,
            R=bool,
            P1=Object *,
            P2=StringName &
        ]
C:\Users\Alex\Desktop\Godot_v3.1.1-stable_mono_win64\godot master\godot\core/class_db.h(225): note: see reference to function template instantiation 'MethodBind *create_method_bind<AStar,bool,Object*,StringName&>(R (__cdecl AStar::* )(P1,P2))' being compiled
        with
        [
            R=bool,
            P1=Object *,
            P2=StringName &
        ]
core\math\a_star.cpp(1605): note: see reference to function template instantiation 'MethodBind *ClassDB::bind_method<MethodDefinition,bool(__cdecl AStar::* )(Object *,StringName &)>(N,M)' being compiled
        with
        [
            N=MethodDefinition,
            M=bool (__cdecl AStar::* )(Object *,StringName &)
        ]
C:\Users\Alex\Desktop\Godot_v3.1.1-stable_mono_win64\godot master\godot\core\method_bind.gen.inc(1784): error C3861: 'convert': identifier not found
scons: *** [core\math\a_star.windows.tools.64.obj] Error 2
scons: building terminated because of errors.

[KnightNine]

Nevermind i found that result.get_type() != 21 needed to be result.get_type() != Variant::POOL_INT_ARRAY and everything else works as it should.
though i still need an answer to //how do I check the number of parameters of the straight_line_function is 2?