How to initialize an object array as a class property?

Question

Sigurd Askeland 2018-4-20

1
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/396260-how-to-initialize-an-object-array-as-a-class-property

评论： Steven Lord 2022-7-21

Here are two code snippets illustrating my problem:

classdef SomeClass
    properties
        foo;
        bar;
    end
end

and in another file:

classdef SomeOtherClass
    properties
        %Array of SomeClass objects.
        someClassArray;
    end
      methods
          function obj = SomeOtherClass(n)
              %Initialize the array, as n can be large.
              obj.someClassArray(n,1) = SomeClass();
          end
      end
  end

When initializing an object of the second class, Matlab assusmes the someClassArray property is a double, and gives an error:

The following error occurred converting from SomeClass to double:
Conversion to double from SomeClass is not possible.
Error in SomeOtherClass (line 10)
          obj.someClassArray(n,1) = SomeClass();

How do I get around this?

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Answer 1

Matt J 2018-4-20

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/396260-how-to-initialize-an-object-array-as-a-class-property#answer_316232

编辑：Matt J 2018-4-20

在 MATLAB Online 中打开

      methods
         function obj = SomeOtherClass(n)

               tmp(n,1)=someClass;
              obj.someClassArray=tmp;

          end
      end

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Jon 2022-7-21

在 MATLAB Online 中打开

I have been experiencing the same problem, and this approach also solves my problem. I am wondering though why it is necessary, or why it works when simply initializing the property value directly i.e

obj.someClassArray(n,1) = SomeClass();

doesn't work.

Steven Lord 2022-7-21

It's because of how property default values are determined. See the "Property Default Values" section on this documentation page for more information.

I'd probably solve this by making someClassArray either a scalar SomeClass object or an empty SomeClass object array (like Prop4 in the documentation section I referenced above.)

But be careful with this if you initialize a property value to an instance of a handle class. See the "Initializing Properties to Handle Objects" section on that same documentation page.

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