Overloading subsasgn results in error when initializing an object array

Question

B Verhaar 2017-8-17

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回答： Steffen M. 2018-2-11

Good day

I have made a class in which I overload the subsasgn method.

classdef dummyClass
    properties
        A = [1, 2]
    end
      %%overload subsasgn
      methods
          function obj = subsasgn(obj, s, varargin)
              % subsasgn is overloaded to incorporate some verifications
              %%TODO some verifications
              %%execute the assignment
              % call the builtin with the same arguments
              obj = builtin('subsasgn', obj, s, varargin{:});
              %%TODO some more verifications
          end
      end
  end

Then I want to initialize an array of dummyClass objects using the following code

clear all
dummyArray(3, 2) = dummyClass()

This gives the following error message:

Error using subsasgn
The following error occurred converting from dummyClass to double:
Error using double
Conversion to double from dummyClass is not possible.
Error in dummyClass/subsasgn (line 15)
            obj = builtin('subsasgn', obj, s, varargin{:});

How can I overload the subsasgn method such that the given assignment does not result in an error?

Kind regards

Boudewijn Verhaar

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Answer 1

Veda Upadhye 2017-8-22

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Hi,

It looks like the overloaded "subsasgn" function is being called on initialization of your "dummyClass" objects. The overloaded function "subsasgn" will need to address this kind of assignment in your code. The documentation below includes a code pattern for such scenarios. You may find it useful to follow a similar pattern.

https://www.mathworks.com/help/matlab/matlab_oop/code-patterns-for-subsref-and-subsasgn-methods.html#bu7rrmd

I hope this helps!

Veda

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Answer 2

Steffen M. 2018-2-11

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在 MATLAB Online 中打开

Hi,

in your case the subsasgn function is called at the beginning with an object from type double. If you insert a constructor call it should work.

function obj = subsasgn(obj, s, varargin)
    if isnumeric( obj), obj = dummyClass(); end
    % call the builtin with the same arguments
    obj = builtin('subsasgn', obj, s, varargin{:});
  end