MATLAB OOP - redefine static method

Hi folks,

Following is an OOP question from a guy who knows nothing about OOP, so excuse me in advance :)

There is a built-in MATLAB class, located in matlabroot/toolbox/coder/connectivity/+coder/+rtiostreamtest/Parameters.m (if your version of MATLAB is earlier than R2012b, you might not find it). This class defines a method called getParameterInstance as Static. I just need to add another case to switch statement in this method. I don't want to modify the shipping MATLAB file, and i heard you can "subclass" those shipping classes.

Following documentation, i created a subclass like this:

classdef Parameters < coder.rtiostreamtest.Parameters
    methods (Static)
        function instance = getParameterInstance(tag, input)
          ..my very own version of switch-case..
        end
    end
end

This subclass is located in +myclass/Parameters.m file in MATLAB path. I then issued "rehash toolbox", just in case.

However, i don't see any effect. I'm not overriding the static method of coder.rtiostreamtest.Parameters class.

What am i doing wrong?

Many thanks!

[Matt J]

However, i don't see any effect... What am i doing wrong?

Maybe nothing. What effect did you try to produce and how?

[Mikhail]

I'm trying to extend existing rtiostreamtest implementation by adding my own connection type. I can do this easily by just adding another case to the switch statement in the getParameterInstance method.

However, i don't want to modify the built-in MATLAB files, hence the question.

After adding another switch case, i'll be calling the rtiostreamtest with my new connection type: rtiostreamtest('shmem','arg1','arg2')

[Matt J]

We need to see the code you executed, a description of what result you got, and a description of what you expected to get.

Answer 1

[per isakson]

Do you use a call like this?

    myclass.Parameters.getParameterInstance( 'two', 'args' )

[Mikhail]

No, the getParameterInstance can't be called directly like that. It is called from rtiostreamtest script (toolbox/coder/connectivity/rtiostreamtest.m).

Your comment though made me think about how MATLAB would know about my class anyway. Probably i would have to modify rtiostreamtest to call to my class instead of the built-in.

Therefore, it would still require to change MATLAB files. I thought it should be somehow possible to use subclassing to override built-in classes transparently, but i was wrong.

[Mikhail]

Ok, i just created a hierarchy +coder/+rtiostreamtest/Parameters.m in a path higher than built-in. So when rtiotreamtest calls to getParameterInstance, it calls to my class instead of built-in.

Still, this has nothing to do with subclassing. Just an override based on how MATLAB resolves commands.

But it's good enough for me. I achieved what i wanted without changing MATLAB files.

Thanks per isakson, nice hint!

[per isakson]

I don't have access to the Embedded Coder toolbox.

Had the call in the "rtiostreamtest script" been

    Parameters.getParameterInstance( 'two', 'args' )

it would have been possible to put a class named Parameters in the top of the Matlab search path. (Not in a package.)

Yes, you will probably need to modify the Matlab script, which should be avoided:-(.

AFAIK: the term built-in class does not include m-files, i.e. not code written in the Matlab language. However, I cannot find a proper definition in the documentation.

[Mikhail]

Well, the "rtiostreamtest script" has

     paramsClass = 'coder.rtiostreamtest.Parameters';

in it, so the path is fully qualified (if that's how it's called).

But as i said earlier, creating the +coder/+rtiostreamtest directory hierarchy higher in MATLAB path with my modified version of Parameters.m did the job.

Oh, sorry if i used built-in term incorrectly. I probably meant shipping.