Method chaining unexpected behaviour?

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Benjamin Chen
Benjamin Chen 2017-12-19
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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采纳的回答

Philip Borghesani
Philip Borghesani 2017-12-20
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
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
Benjamin Chen 2017-12-20
That's great news, looking forward to it!

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更多回答（1 个）

Image Analyst
Image Analyst 2017-12-19
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 个评论
Benjamin Chen
Benjamin Chen 2017-12-19
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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