MATLAB: How to use a class property validation function with a dynamic argument

MATLABoop

In Matlab OOP, I wanna use a function like mustBeEqualSize(a,b) from the Examples on function property validation to validate a property:

classdef foo
    properties
        a
        b {mustBeEqualSize(a,b)}
    end
end

However, this gives me an error.

Best Answer

The problem is, that MATLAB classes only support constant arguments on property validation.

However function arguments can be validated perfectly fine with dynamic arguments.

So a workaround is to validate the arguments of the constructor:

classdef Foo
    properties
        a
        b
    end
    
    methods
        
        function obj = Foo(a,b)
            arguments
                a
                b {mustBeEqualSize(a,b)}
            end
            obj.a = a;
            obj.b = b;
        end
    end
end

Related Solutions

MATLAB: Access property of “superior” class (not superclass)

There is not really a term to describe your relationship between A and B other than to say that A has a member variable that is an instance of B.

It is of course not possible to access any private properties or methods of A from B. That is the whole tenet of encapsulation in OOP. Only the class (or derived classes) can access private members.

B can of course access any public member of A, and it can also access any member for which you give it explictly access (see the doc).

Now for an instance of B to access a member (public or one it's been granted access to) of the A instance that holds it, it needs itself to hold a reference to that A (hence A have to be a handle class). Therefore you would need:

classdef A < handle
   properties (SetAccess = private, GetAccess = ?B) %B (and A of course) can read it
      prop1 = 7; %property to be read by B
   end
     properties (SetAccess = private)
        propB; %hold B instances
     end
     methods
        function this = A()  %constructor

            this.propB = B(this); %pass a reference to self to B constructor
        end
     end
  end
classdef B
   properties (Access = private)
      owner; an instance of A
   end
     methods (Access = ?A) %only A can construct B?
        function this = B(Ainstance)  %constructor
           this.owner = Ainstance;
        end
     end
     methods
        function delete(this)  %destructor. not sure it's needed.
           this.owner = [];
        end
        function method_that_uses_A(this)
           disp(this.owner.prop1)
        end
     end
  end

Then:

a = A;
a.propB.method_that_usesA

displays

MATLAB: Property validation in subclass

Note: I would recommeng giving a name other than set to your property. That name is already overloaded enough by matlab.

You can create a property validation function in the class that define the property using the syntax (for handle classes):

function set.propertyname(object, valuetoset)
    %validation code
end

with your property name this would be

function set.set(this, value)     %See why you should rename the property?
   if ~strcmp(class(value), somevalidclass)
        error('invalid class supplied to set');
   end
   this.set = value;
end

However, as I said, this property set method must be implemented in the class that defines the property, that is your base class, not the derived class. The workaround is from the set method to call another method that does the validation and is overridden by the derived class:

classdef SimpleList < handle
    properties
        set;
    end
      methods
          function set.set(this, value)
              isok = this.validateset(value);  
              if ~isok
                 error('invalid type of variable for set property)
              end
              this.set = value;  %DO NOT set the value is a subfunction or you'll get infinite recursion
          end
      end
      methods (Access = protected)
          function isok = validateset(this, value)
             isok = true;
          end
      end
  end
classdef ObjList < SimpleList
    methods (Access = protected)
        function isok = validateset(this, value)
           isok = strcmp(class(value), 'double');
        end
    end
end

Best Answer

Related Solutions

MATLAB: Access property of “superior” class (not superclass)

MATLAB: Property validation in subclass

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