How can I use NARGIN/NARGOUT to determine the number of input/output arguments of an object method?

조회 수: 50(최근 30일)
I am trying to determine the number of input/output arguments of an object's method. When the name of any object method is passed to NARGIN/NARGOUT, the returned value is always -1 regardless of the number of inputs/outputs specified in the method signature.
The following syntax returns -1 for any MethodName:
nargout('MethodName')

채택된 답변

MathWorks Support Team
MathWorks Support Team 2010년 9월 20일
The ability to call NARGIN/NARGOUT directly on object methods is not available in MATLAB. As a workaround, specify the class and method names explicitly using the following syntax:
nargout('ClassName>ClassName.MethodName')

추가 답변(3개)

Eric Salemi
Eric Salemi 2018년 7월 12일
편집: Eric Salemi 2018년 7월 12일
I suggest you use the meta information provided by the MCOS class system:
>> class = ?containers.Map;
>> method = class.MethodList({mclass.MethodList.Name} == "subsref");
>> method.InputNames
ans =
2×1 cell array
'A'
'S'
>> method.OutputNames
ans =
cell
'B'
It is reliable in most cases except when your class definition uses the old-style @ folder or if you query a non-MCOS class such as a Java class or such. On the side note, the accepted answer will not work for a qualified class such as above, which just shows that the NARGIN/NARGOUT functions are function-oriented are have not been adapted for the MCOS class system.
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Gunter Nitzsche
Gunter Nitzsche 2022년 8월 3일
I really like this appraoch. Surprising for me was that you really have to use the double quotes around "subref" as otherwise you get an error Undefined operator '==' for input arguments of type 'cell'.

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Markus Leuthold
Markus Leuthold 2015년 4월 16일
It's almost five years later and this bug still exists. Any news from Mathworks on how to handle this situation in 2015?
Example:
Class C
classdef C < handle
methods
function r=fcn1(~)
r='run fcn1';
end
function fcn2(~)
disp('run fcn2');
end
end
end
function run
function run(f)
switch nargout(f)
case 0
feval(f);
case 1
disp(feval(f));
case -1
disp('bug')
end
What I expect from the following code
>> c=C;
>> run(@c.fcn1)
run fcn1
>> run(@c.fcn2)
run fcn2
Instead I get
>> c=C;
>> run(@c.fcn1)
bug
>> run(@c.fcn2)
bug
How do you recommend to workaround in case where you want to know nargout from a function handle AND evaluate a function handle?

Christopher Hummersone
Christopher Hummersone 2015년 9월 18일
An indirect solution is to test for the existence of a particular variable:
exist('var_name','var')==1
This works for input variables; I haven't tested it for output variables.
  댓글 수: 1
Madhav Rajan
Madhav Rajan 2016년 2월 2일
Although it helps, with exist you will need to the know the names of the variables that you want to track. NARGIN/NARGOUT makes it easier since you do not need any book keeping.

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