Object Oriented Programming - Leaving properties from objects empty.

Hi everybody! I am writing the following code:

    classdef Value0_1
        properties
            Price
            Earnings
            ddd
            BookValue
            P_E_Calc
            P_B_Calc
        end
        methods
            function PE=Value0_1(price,earnings,Ddd)
                if nargin <2
                    PE.Price=price;
                    PE.Earnings=earnings;  
                    PE.ddd=Ddd;
                end
            end
        end
    end

Now, I would like to create an object by typing in the command Window PriceEarnings=Value0.1(555,555,~). the following error comes: Error: Invalid expression. When calling a function or indexing a variable, use parentheses. Otherwise, check for mismatched delimiters.

--> How can I leave the argument Ddd empty?

Answer 1

[Matt J]

The call should look like PriceEarnings=Value0_1(555,555) and the code for the constructor should look like,

             function PE=Value0_1(price,earnings,Ddd)
                if nargin >=1
                    PE.Price=price;
                end
                if nargin>=2
                    PE.Earnings=earnings;
                end  
                if nargin>=3
                    PE.ddd=Ddd;
                end
            end

[Matt J]

Bruno commented

Thank you for your rapid answer. What if I want to create an object leaving the fist argument of the function Value0_1 empty, the second with numbers and the last one empty again. I need to create several objects.

[Matt J]

You would just do,

PE=Value0_1([],earnings,[])

or

 PE=Value0_1([],earnings)

[Matt J]

You might also think about using inputParser, to make all the parameters non-positional.

[Adam]

I tend to use

if exist( 'earnings', 'var' ) && ~isempty( earnings )
   validateattributeS( earnings,... )
else
   earnings = someDefaultValue;
end

nowadays rather than using nargin, for this purpose. Then I pass in empty, like Matt J has done which causes it to use the default value I supply. I occasionally use the inputParser, but I've generally only done it when I allow 'name', 'value' pairs of any of my properties to be set like in many Matlab functions.

Answer 2

[BdS]

Thanks a lot Adam and Matt. I am quite new in OOP. Therefore I would like the following question. In my project the objects (=stock factors) have different properties depending on which factor you choose. The classes corresponds to Styles (=families of stock factors). This means that everytime when I create a factor, some properties stay empty (without values) which I really do not know if this is common? Do you know a better method of solving this task with matlab?

[Adam]

It's hard to know without more specific examples, but you can create class hierarchies where a derived class will extend the base class, which sounds like what you may want, for the extra properties that may be empty in some objects otherwise. Obviously if every property is different then you would just want two independent classes, but I am assuming there is commonality too.