Property Validation fails due to assignment issues.

Hey everyone,

I'm trying to implement some property validation function for a class as follows

classdef test

   properties
      Str {mustBeString(Str)}
   end

   methods
       function obj = test(str)
           obj.Str = str;
       end
   end
end

function mustBeString(str)
    % MUSTBESTRING checks if argument is a string
    if ~isstring(str) && ~ischar(str)
        error('Parameter:wrongType',...
            'Description must be string.');
    end
end

But here's the problem. It doesn't matter which value or type Str has, because matlab seems to assign an empty value for this property even before the constructor is evaluated. In fact I checked in debugging mode and it seems that the validation function is called before the constructor.

I also tried to execute a modified example from the matlab documentation

classdef ImData
   properties
      Data {mustBeNumeric, mustBeInRange(Data,[0,255])}
   end

     methods
        function obj = ImData(dat)
          obj.Data = dat;
        end
     end
  end
  function mustBeInRange(a,b)
     if any(a(:) < b(1)) || any(a(:) > b(2))
        error(['Value assigned to Data property is not in range ',...
           num2str(b(1)),'...',num2str(b(2))])
     end
  end

In this case everything worked fine.

Anyone who might have an idea, how to fix this issue?

Thank you very much.

Answer 1

[Nirav Sharda]

The documentation page of Property Validation mentions that you should add a default value. Also in the example mentioned in the document they have set the default value of the Data which is numeric to 0. You can in your case set it to empty string or char array. You can modify your code to:

Str {mustBeString(Str)} = ''

I hope this helps.