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Method chaining unexpected behaviour?

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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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Accepted Answer

Philip Borghesani
Philip Borghesani on 20 Dec 2017
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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Benjamin Chen
Benjamin Chen on 20 Dec 2017
That sounds reasonable, thanks. I wish the error message could have been this informative rather than just "Not enough input arguments".
Philip Borghesani
Philip Borghesani on 20 Dec 2017
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
Benjamin Chen on 20 Dec 2017
That's great news, looking forward to it!

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More Answers (1)

Image Analyst
Image Analyst on 19 Dec 2017
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);

  1 Comment

Benjamin Chen
Benjamin Chen on 19 Dec 2017
Thanks for the answer Image Analyst. It seems the error is not at the fprintf part, but in the static getB method of class A.
Even if I replace the fprintf with disp, it still gives the same error.

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