OOP in MatLab -- assigning values to properties?

Question

Sam Butler 2013-10-16

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/90398-oop-in-matlab-assigning-values-to-properties

评论： Daniel Shub 2013-10-16

I am trying to understand how MatLab does OOP in R2013b, so I got started with a simple test class, but it doesn't seem to behave as desired. The test class has 2 properties, A and B, which I keep at default scope (which I believe is public). I used the following class definition, with default values:

classdef classtest
      properties
          A = 0;
          B = uint64(5);
      end
      methods
          function changeA(obj, newA)
              obj.A = newA;
          end
          function changeB(obj, newB)
              obj.B = newB;
          end
      end
end

Then I run the following code, with outputs shown:

>> a=classtest;
>> a
a = 
    classtest with properties:
      A: 0
      B: 5
>> a.changeA(128);
>> a.changeB(256);
>> a
a = 
    classtest with properties:
      A: 0
      B: 5
>>

The values of A and B have not updated based on the method executed, but are instead still their default values.

What am I doing wrong?

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Answer 1

Sean de Wolski 2013-10-16

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https://ww2.mathworks.cn/matlabcentral/answers/90398-oop-in-matlab-assigning-values-to-properties#answer_99865

编辑：Sean de Wolski 2013-10-16

在 MATLAB Online 中打开

Your class is not a handle class but rather a value class. Thus when you run:

a.changeB(256);

A new variable ans in your workspace will exist with the change. If you want to update the value in this a and keep it as a value class, assign the output back to a:

a = changeA(a,128)

Or change your class to a handle class. It really depends on what you plan to do with this class as to whether you want it as a handle or value class:

classdef classtest < handle

http://www.mathworks.com/help/releases/R2013b/matlab/object-oriented-design-with-matlab.html

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Sean de Wolski 2013-10-16

That sounds about right!

The only time I use value classes is when I want them to behave, well I guess, as values. A simple (e.g. double or uint8) matrix is a value class because when you pass it into the function, the function cannot change it. So when making a class that will behave like a matrix, I would use a value class.

Daniel Shub 2013-10-16

For the OP's definition of changeA, a = changeA(a,128) gives an error. It is worth pointing out that the handle/value class issue is flagged by mlint.

@Sam As for value and handle classes, I think the polynomial class example in the documentation highlights a good use case of a value class.

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