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BdS
0

Object Oriented Programming - Leaving properties from objects empty.

Asked by BdS
on 28 Aug 2018
Latest activity Commented on by Adam
on 29 Aug 2018
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?

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2 Answers

Answer by Matt J
on 28 Aug 2018
Edited by Matt J
on 28 Aug 2018
 Accepted Answer

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

  4 Comments

Show 1 older comment
You would just do,
PE=Value0_1([],earnings,[])
or
PE=Value0_1([],earnings)
You might also think about using inputParser, to make all the parameters non-positional.
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.

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Answer by BdS
on 29 Aug 2018

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?

  1 Comment

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.

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