Custom exceptions private methods

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Benjamin Chen 2018-1-12

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https://ww2.mathworks.cn/matlabcentral/answers/376894-custom-exceptions-private-methods

评论： Benjamin Chen 2018-1-12

I would like to raise a custom error/exception when a user tries to call a private method/constructor. Suppose I have a class:

 classdef MyClass
    methods (Access = private)
        function self = MyClass(arg1, arg2)
          % Some constructor logic
        end
    end
    methods (Static)
        function myClass = createMyClass(arg1, arg2)
             myClass = MyClass(arg1, arg2)
         end
    end
end

If I try to call:

MyClass(arg1, arg2)

it gives a not so helpful error:

Error using MyClass
Cannot access method 'MyClass' in class 'MyClass'.

I would instead like to point the user to the static method by saying:

'Construct me by calling MyClass.createMyClass.'

How would I be able to do this? Thanks!

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Adam 2018-1-12

You can customise error messages by rethrowing errors but I can't think of a way off-hand that doesn't require you to know in the first place that the code you are writing (i.e. accessing the constructor) is incorrect in order to catch the exception it throws, in which case it is pointless as you would just correct it anyway.

I have never had any objection to the default message myself - it is succinct and to the point and you can easily query class methods or look in the class definition to work out what to call instead.

Benjamin Chen 2018-1-12

I agree that generally the default message would be fine if I would be the only one using these classes or if users would look into these classes and read the documentation.

I would like however to make these classes as user friendly as possible. Sometimes it is also not obvious what should be called e.g. if I am using a builder pattern and the class is created by a separate builder class, then I think having the ability to point the user to that would be a useful feature to have.

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