What am I doing wrong with object oriented programming?

This is hopefully a very straight forward problem. I've tried looking through the documentation, but everything I'm doing seems legit so here I am.

I have a .m file ParticleInBox.m

 classdef ParticleInBox

    properties
    end

    methods
        function q = calculateSin(x)
           q = sin(x); 
        end
    end

If I try

>> p = ParticleInBox();
>> p.calculateSin(2.0)
Error using ParticleInBox/calculateSin
Too many input arguments.

Any ideas why it is complaining about too many input arguments?

Thanks!

Mark

Answer 1

[Sven]

Mark, you're almost there. Here's how to "just get it running":

    methods
        function q = calculateSin(this, x)
           q = sin(x); 
        end
    end

Note that I've added an argument to your function. The first argument of all functions of a class will be the instance of that class being called. So when you call:

>> p = ParticleInBox();
>> p.calculateSin(2.0)

The second line is actually equivalent to:

calculateSin(p,2.0)

One way to think of what happens is that MATLAB basically checks the first argument of every call to a function. If that first argument is an object (as in your case, the object is p), and that object is of a class that has a method equivalent to the function being called (in your case the object p is of the class ParticleInBox, which has a method called calculateSin), then MATLAB will call that method, giving the object itself (ie, p) as the first argument.

So to answer your question, your original function signature had only one argument, which is by default the object (even though you used the variable name x). When you called the function with a second argument 2.0 you gave it more arguments than it expected.

[Mark]

Excellent answer! Thanks a lot Sven.