Using abstract classes in Matlab (without properties)

Question

Let we have one abstract class:

classdef ACalculation < handle

    methods (Abstract)
        [result] = calculate (this, data);

        plot (this, data, limX, limY);
    end

end

And some other classes that implements ACalculation

classdef Maximum < ACalculation

    methods
        function [result] = calculate (this, data)
            %...
        end

        function plot (this, data, limX, limY)
            %...
        end
end

To functions of implementation class i give all needed information, so i don't need any properties. So it looks like I need static classes. But if I have static classes I have a problem with calling this functions. I'd like to do something like that:

criteria = Maximum();
%......
result = criteria.calculate(data);

Is it bad way to use inheritance? Should I ignore matlab advices to change functions to static? What else could I do here?

Andrey Rubshtein · Accepted Answer · 2012-03-21 09:03:09Z

I think that in this case, static interface implementation is quite a good pattern. Define your classes in the following way:

classdef ACalculation < handle

    methods (Abstract,Public,Static)
        [result] = calculate (data);    
        plot (data, limX, limY);
    end

end

classdef Maximum < ACalculation

    methods (Public,Static)
        function [result] = calculate (data)
            %...
        end

        function plot (data, limX, limY)
            %...
        end
end

Then, you can write a function that expects an ACalculation type:

 function foo(acalc,data)
      assert(isa(acalc,'ACalculation'));
      acalc.calculate(data);
      acalc.plot(data,[100 200]);
 end

Then create a Maximum empty instance and pass it to foo:

 foo ( Maximum.empty(0), [1 2 3]);

If you want to change the calculation method, call

 foo ( Minimum.empty(0), [1 2 3]);

When you say that such a pattern will not work, you are thinking like Java/C#/C++ developer. But unlike in C++ where static and virtual keyword cannot coexist, Matlab has no such limitation, because everything is done at runtime, and an "instance" can be empty or an array of n elements.

Sam Roberts · Accepted Answer · 2012-03-20 12:27:36Z

0

If calculate is a static method of Maximum‘, you would use ‘result = Maximum.calculate(data) to call it, without instantiating to criteria.

It's not (necessarily) a bad way to use inheritance, or bad advice from MATLAB.

answered Mar 20, 2012 at 12:27

Sam Roberts

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1 Comment

Lex Over a year ago

But if I have also other classes (Minimum, Mean and so on) i'd like to choose somewhere in the beginning wich type is used and after that using some object of abstract class, without saying which exactly class it is. In this case I can't use static, isn't it?

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