Passing varargin to nested class method in MATLAB - matlab

Question

I would like to parse variable inputs for several class methods in the same way, so I wrote a method to do just that and intend to call it from the other methods as needed. However, when I call methodB from methodA, varargin{:} isn't being passed as its cell contents but as another cell array – similar to if I hadn't included the {:}.
Does anyone have an idea why the contents aren't passing?
methods
function varargout = methodA(obj,varargin)
[obj,t.start,t.stop,prn,elevLim,t.interval] = methodB(varargin{:});
end
function varargout = methodB(varargin)
% parse inputs here...
%output parsed inputs to calling function
varargout = {obj,t.start,t.stop,prn,elevLim,t.interval};
end
end

Answer 1

When you try to use your code as stated in the question, you will get error messages which would have been valuable to mention. In case you write methodB(varargin) this message is:
Undefined function 'methodB' for input arguments of type 'double'.
And when writing methodB(varargin{:}) it is:
Undefined function 'methodB' for input arguments of type 'cell'.
The main problem here is that you have not explicitly defined the first argument of methodB to be an object variable. This is needed since methodB is a so-called ordinary method because it is not defined as static. There are some other problems in the code as well. For example methodA never assigns something to varargout and methodB should return obj which is not defined neither.
Solution with ordinary method
methodB needs to have an explicitly defined object variable, so the first line of the definitition should be: function varargout = methodB(obj,varargin). However, if we don't need obj in the method itself, we can replace it with ~, so it dosen't get assigned to a variable.
In order to call the method you need to use the proper syntax to call it, either methodB(obj,varargin{:}) or obj.methodB(varargin{:}).
Here is working code to verify it:
classdef nestedvarargin
properties
end
methods
function varargout = methodA(obj,varargin)
[t.start,t.stop,prn,elevLim,t.interval] = methodB(obj,varargin{:}); % call ordinary method (syntax 1)
% [t.start,t.stop,prn,elevLim,t.interval] = obj.methodB(varargin{:}); % call ordinary method (syntax 2)
varargout = {t.start,t.stop,prn,elevLim,t.interval};
end
function varargout = methodB(~,varargin)
% extract desired values from varargin (for example leave 3rd argument out)
varargout = {varargin{1},varargin{2},varargin{4},varargin{5},varargin{6}};
end
end
end
Solution with static method
The other way is to define methodB to be static and call it as baseclass.methodB(varargin{:}). In this case, no explicitly defined object variable is needed.
The code looks like this:
classdef nestedvarargin
properties
end
methods
function varargout = methodA(obj,varargin)
[t.start,t.stop,prn,elevLim,t.interval] = nestedvarargin.methodB(varargin{:}); % call static method
varargout = {t.start,t.stop,prn,elevLim,t.interval};
end
end
methods(Static)
function varargout = methodB(varargin)
% extract desired values from varargin (for example leave 3rd argument out)
varargout = {varargin{1},varargin{2},varargin{4},varargin{5},varargin{6}};
end
end
end
Testing
In order to verify the functionality, you can use the following two lines. As defined in methodB, the third argument should be omitted as well as the arguments after the sixth (5 in the case below).
testobj = nestedvarargin;
[a,b,c,d,e] = testobj.methodA(1,2,[],3,4,5,[])
The output is be as expected:
a =
1
b =
2
c =
3
d =
4
e =
5