Method chaining unexpected behaviour?

Question

Benjamin Chen 2017-12-19

1
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/373751-method-chaining-unexpected-behaviour

评论： Benjamin Chen 2017-12-20

I have noticed some unexpected behaviour with method chaining. Specifically I have a class A from which I want to call the static method to create class B:

classdef A
  methods (Static)
      function b = getB(args)
          b = B(args);
      end
  end
end

And then I want to use class B to do something e.g. use the print() method, where class B is:

classdef B
  properties
      Property1
  end
    methods
        function self = B(args)
            self.Property1 = args;
        end
        function print(self)
           fprintf(self.Property1); 
        end
    end
end

Trying

A.getB(args).Property1

succeeds.

I would thus also expect

A.getB(args).print()

to succeed, however, it gives the error:

Not enough input arguments.
Error in A.getB (line 5)
          b = B(args);

Would anyone have any suggestions on why this is so? Thanks very much in advance.

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Answer 1

Philip Borghesani 2017-12-20

1
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https://ww2.mathworks.cn/matlabcentral/answers/373751-method-chaining-unexpected-behaviour#answer_297143

在 MATLAB Online 中打开

In general indexing into the output of a function call, what you call method chaining is not supported in MATLAB. Property access currently works on the output of a static function but function calls in general do not. You may find that your code behaves differently on different versions of MATLAB.

Try

 A.getB(args).print;  % works because it looks like property access, not recommended
 print(A.getB(args));  % will work
 obj=A.getB(args); obj.print();  % or print(obj) will also work

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Philip Borghesani 2017-12-20

I agree, the error message should have been better.

This appears to be fixed so that a static call works correctly in a future version of MATLAB.

Benjamin Chen 2017-12-20

That's great news, looking forward to it!

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Answer 2

Image Analyst 2017-12-19

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/373751-method-chaining-unexpected-behaviour#answer_296984

在 MATLAB Online 中打开

fprintf(self.Property1);

needs two inputs, a format string, and a variable. You only passed it the variable without passing it a format specifier string like '%f\n' or something (depends on the type of variable you want to print).

fprintf('The value = %f\n', self.Property1);