Error : "Check for incorrect argument data type or missing argument in call to function 'spawnTorpedo'."

I'm trying to create a simple class for a game project I'm doing for school. Torpedo is just an object that has a position and a direction that it's facing. If I try to test the functions (ie. t = spawnTorpedo(2,3,4,5) I get the error "Check for incorrect argument data type or missing argument in call to function 'spawnTorpedo'." Any help would be appreciated.

classdef torpedo
    properties
        x
        y
        xdir
        ydir
    end
    methods
        function torp = spawnTorpedo(xStart,yStart,cursorX,cursorY)
            dir = [cursorX - xStart, cursorY - yStart];
            dir = dir/norm(dir);
            
            torp.x     = xStart;
            torp.y     = yStart;
            torp.xdir  = dir(1);
            torp.ydir  = dir(2);
        end
        
        function objOut = moveTorpedo(objIn,speed)
            objOut.x = objIn.x + objIn.xdir*speed;
            objOut.y = objIn.x + objIn.ydir*speed;
        end
    end
end

Answer 1

[Dave B]

spawnTorpedo is a (non-static, non-constructor) method, so the first argument should be the object:

obj = torpedo;
obj.spawnTorpedo(2,3,4,5)

(Alternatively, with MATLAB objects, you can use a function like syntax)

spawnTorpedo(obj,2,3,4,5)

And the signature should be:

function torp = spawnTorpedo(torp,xStart,yStart,cursorX,cursorY)

Unless it's the constructor (which was maybe the intent), in which case the signature should be:

function torp = torpedo(xStart,yStart,cursorX,cursorY)

and you should call it as:

thistorp = torpedo(2,3,4,5)

[leonard_laney]

Thanks so much! If i wanted to pass an object by reference, would I have to redefine the whole class? Like say i wanted to redefine position using the moveTorpedo function, can I do that without making a copy of the torpedo?

[Dave B]

MATLAB has a pretty different approach to how you do this than other languages.

If you define your class as a handle class (this means subclass from handle):

classdef torpedo < handle

Then objects of the class are always treated as references:

a=torpedo; % ignoring your constructor arguments
a.x=1;
b=a;
b.x=2;
a.x %will be 2, a and b both point to the same instance

If you make torpedo a handle class, then your move function will look like:

function moveTorpedo(obj, speed)
    obj.x = obj.x + objIn.xdir*speed;
    obj.y = obj.y + objIn.ydir*speed; %note I fixed a typo here where you had an x but I suspect wanted a y!
end

Then you can just do:

torp1=torpedo;
torp.moveTorpedo(10);

If your class isn't a handle class, then you have to create a copy when you move it (although it's certainly possible that there will be an optimization under the hood that prevents this from being expensive).