Hello,

In Object-Oriented Programming methodology, construction function is used to assign the data to the object variables. But in the following Matlab code, there is a structure in the constructure function and I am trying to understand this usage and how we can interpret the logical operators in the code below.

I am not sure if this is the right place asking this kind of question here but if you could explain I would be glad.

Here are my questions:

1-Could you please explain how it works and why a structure is used in the constructor function above?

2-In the constructor function there is a tilde (~) operator, how do we interpret the usage of this tilde operator here?

3-Is there any other way that can be used to express the same purpose here instead of using tilde?

4-Also could you please help interpreting the usage of isstruct operator in the constructor function?

5-What is the meaning of (~isfield(StructParameters)) logical function?

Many thanks in advance!!!!

classdef myClass
    properties
        a;
        d;
        noInput;
    end
    methods
        function obj=myClass(StructParameters)
            if nargin==0
                StructParameters.noInput=1;
            else
                StructParameters.noInput=0;
            end
           
            if ~isstruct(StructParameters)
                error('Input argument has to be struct.')
            else
                % load the parameters
                F=fields(StructParameters);
                for x=1:length(F)
                    obj.(F{x})=StructParameters.(F{x});
                end
            end
                    
            if ~isfield(StructParameters, 'a')
                obj.a=[1 2; 4 5];
            end
   
           if ~isfield(StructParameters, 'd')
                obj.d=[0 1; 4 5];
            end
        end
       
     end
   
end

1: I'm not sure exactly what they're attempting, but it looks like they're constructing a structure F that matches the input structure.  The "why" is because sometimes you want to pass in structured data; more than that would have to come from the author.

2: The tilde in Matlab is a logical not: for a scalar, (a == 1) is the same as ~(a~=1) (this may or may not be the case if a is a vector -- trying to figure that out without doing a bunch of test cases would make my brain hurt).

3: Probably not, or at least it'd be dangerous.  If the "isfield" function is strict about returning a boolean, then you could say "isfield(whatever)==false", where 'false' in this context is whatever Matlab predefines as being a logical false (I'm not a Matlab guy: in Scilab it's '%F').

4: By context, it pretty much has to mean that it's telling you whether the argument is a structure or not.

5: isfield(StructParameters, 'a') will, I'm 99.44% certain, return true if the structure has a field named a.  ~isfield(StructParameters, 'a') should return false if the structure has a field named a, and true if it does not.  isfield(StructParameters) should probably generate an error message.

Thank you Tim for your quick reply!!!
It is better than yesterday now but still some parts that I am still searching for them.

1- If it is the structured data to be passed into the class
MyClass then how can I access into the structured data, StructParameters?

2-How can I run the following error condition?
   error('Input argument has to be struct.')

Could someone please give me an example commands for this run?

Thanks