still not getting the oop concept... please help

i got the following code:

classdef node
    properties 
        x;
        y;
        bearing=0;
    end % properties
    methods
        function obj = node(x,y)
            obj.x=x;
            obj.y=y;
        end%functions
    end%methods
end %class

classdef manlists 
    properties
        nodelist ;
    end
    methods
        function h   = AddNode(self,a,b) % Add a node with 2 coordinates
            if (isempty(self.nodelist))
                self.nodelist = [node(a,b)];
            else
                self.nodelist(self.grN+1,1) = node(a,b); %grN gives the size of nodeslist
            end
        end
    end
end

lets say i have my instance called man = manlists; if i call it by man.AddNode(1,2) it returns the node buts doesnt store it in man; in other words : i can call man man.AddNode(1,1) as many times i want but the nodelist cantaines just one element;

if i call it by men = man.AddNode(1,2) it does what i want it to do,

the thing is that i have to call this like 10000 times wihin the programm and i gues that this makes it really slow

in C i would use a pointer for this....

does anyone has a sugestion??

thanks a lot

Answer 1

[Kye Taylor]

You can get the behavior you want if you subclass the handle class.

To do this, 1.) replace the line

classdef manlists

with

classdef manlists < handle

and 2.) remove the output from the AddNode() method.

See http://www.mathworks.com/help/techdoc/matlab_oop/brfylq3.html for more info.

[jeff wu]

thanks a lot. am i right in the opinion that my way makes the executement slow because everytime i change somthing in the man instance it has to copy the instance and sent it into the function.

the prorblem is that man has several other instances of other classes organized the same way. isnt there something likewise pointers in c or c++ or some other way.

your solution would work for this problem but if i take the hole code it makes it lot more complicated

thanks again for your answer

[Daniel Shub]

@Jeff One of the reasons your code is slow is that you are creating and destroying things every time (another is that MATLAB OOP is just slow).

High level languages like MATLAB do not need pointers, in essence everything in MATLAB is a pointer and it only copies (allocates new memory for) things when it needs to. Handle classes help MATLAB know that you want to change the current copy, such that everything that points to it also changes, and not to make a new copy.

It is not clear to me why you think it makes your code more complicated.

[Kye Taylor]

@Jeff, it's unclear what is more efficient. I would suggest experimenting with both implementations. It would be interesting to hear what you find works better.

Check out a recent post at <http://blogs.mathworks.com/loren/2012/03/26/considering-performance-in-object-oriented-matlab-code/> for some related information. Bottom line is that this suggests that if you're using loops and calling that method often, it is likely more efficient if you can keep that loop inside the method itself.