How to use static factory method?

Question

Vincent Schmidt 2021-7-13

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/877718-how-to-use-static-factory-method

回答： Greg 2024-5-13

I have following class definition under +mypackage\MyClass.m

classdef MyClass  
    properties
        num
    end
    
    methods (Static)
        function obj = with_five()
            obj = MyClass(5);
        end
    end
    
    methods
        function obj = MyClass(num)
            obj.num = num;
        end
    end
end

I use with_five() as a static factory method.

Following script should create two objects.

import mypackage.MyClass
class_test1 = MyClass(5);
class_test2 = MyClass.with_five();

class_test1 has been created.

For class_test2 it says:

Error using MyClass.with_five
Method 'with_five' is not defined for class 'MyClass' or is removed from MATLAB's search path.
Error in Testpackage (line 4)
class_test2 = MyClass.with_five();

When I put MyClass.m outside of a package folder and remove the "import" statement, it works.

What am I doing wrong?

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Answer 1

Greg 2024-5-13

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/877718-how-to-use-static-factory-method#answer_1456686

在 MATLAB Online 中打开

Old question, but maybe others have seen this and wondered the same thing. Fairly simple answer.

In your factory method, you do not call out the namespace:

obj = MyClass(5);

Needs to be:

obj = mypackage.MyClass(5);

The import is in your test script, not your class. Import statements are extremely localized, so the factory method does not know about a MyClass, only a mypackage.MyClass.