operator overloading: classnumber vs numberclass

Question

Javier Ros 2018-8-29

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/416651-operator-overloading-class-number-vs-number-class

评论： Steven Lord 2018-8-29

采纳的回答： Javier Ros

Hello,

I've defined a class (lets say vector) and I want to be able to overload the following binary operations

1) >> my_class*number

2) >> number*my_class

I have overloaded mtimes, and then case 1) works (I detect the type of the second operator and proceed accordingly), but case 2) does not. In fact the mtimes function of the class does not get called in case 2).

This may seem as logical, but in cannot figure out a work arround for 2).

How do I program behavior for case 2), that is number*my_class ?.

Thanks,

Javier

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Answer 1

Javier Ros 2018-8-29

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https://ww2.mathworks.cn/matlabcentral/answers/416651-operator-overloading-class-number-vs-number-class#answer_334551

在 MATLAB Online 中打开

Solution:

It seems that it is a question of object precedence when invoking the mtimes defined operator.

Changing the definition of my_Class from

classdef my_Class

to

classdef (InferiorClasses = {?sym}) my_Class

gives precedence to my_Class mtimes method against the one of sym class

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Steven Lord 2018-8-29

That is correct. See the first section on this documentation page for an explanation.

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Answer 2

Javier Ros 2018-8-29

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/416651-operator-overloading-class-number-vs-number-class#answer_334542

编辑：Javier Ros 2018-8-29

在 MATLAB Online 中打开

After some more trials I presume this is a BUG related to the symbolic toolbox.

If I do

2.1) >> 5*my_class ---->>>> WORKS it enters the overloaded class function mtimes

2.2) >> syms g real, g*my_class --->>>> FAILS it does not enter the class function mtimes

The error is:

>> g*ez %g is syms g real, and ez is of type my_class
    Error using sym>tomupad (line 1229)
    Unable to convert 'my_class' to 'sym'.
    Error in sym (line 211)
                    S.s = tomupad(x);
    Error in sym/privResolveArgs (line 966)
                        argout{k} = sym(arg);
    Error in sym/privBinaryOp (line 990)
                args = privResolveArgs(A, B);
    Error in  *  (line 312)
            X = privBinaryOp(A, B, 'symobj::mtimes');

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Steven Lord 2018-8-29

No, this is not a bug.

I assume you posted this answer before posting the one that you ultimately accepted, as in the accepted answer you successfully identified how to obtain the behavior you wanted. The comment I posted to that accepted answer points to the documentation page that explains why you see this behavior.

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