validate arguments stop implicit expansion

classdef Car
    properties
        id
        position
    end

    methods
        function obj = Car(id, position)
            arguments
                id (1,1) {mustBeNumeric, mustBePositive, mustBeInteger, mustBeNonempty}
                position (1,3) double {mustBeVector, mustBeNonempty}         
            end
            obj.id = id;
            obj.position = position;
        end
    end
end

myCar = Car(42, 20)

Instantiation of myCar creates position vector [20, 20, 20]. This is because of implicity expansion. I am trying to stop this by adding a custom validator, but having trouble.

Answer 1

[Bhanu Prakash]

Hi Nilay,

If I understand it correctly, you want to ensure that the 'position' argument passed is a vector and thereby avoid implicit expansion.

For this use case, you can simply use a custom function (validatePositionArgument, in this case) to verify that the argument 'position' is a vector. If it's not, then the code throws an error. Here is the modified code:

classdef Car
    properties
        id
        position
    end
    methods
        function obj = Car(id, position)
            validateattributes(id, {'numeric'}, {'scalar', 'positive', 'integer', 'nonempty'}); % validate 'id'            
            validatePositionArgument(position); % custom function to validate position

            obj.id = id;
            obj.position = position;
        end
    end
end

function validatePositionArgument(position)
    % Throws an error if the input 'position' is not a vector or if it's
    % length is not equal to 3.
    if ~isvector(position) || length(position) ~= 3
        error('Position must be a 1x3 vector.');
    end
end

Instantiation of myCar with the 'position' argument as a vector:

>> myCar = Car(42, [10, 15, 20])

myCar = 

  Car with properties:

          id: 42
    position: [10 15 20]

If the 'position' argument is not a vector or if its size is not equal to 3:

>> myCar = Car(42, 20)
Error using Car>validatePositionArgument (line 21)
Position must be a 1x3 vector.

Error in Car (line 9)
            validatePositionArgument(position); % custom function to validate position

For more information on the 'validateattributes' function, you can refer to the following documentation:

https://www.mathworks.com/help/matlab/ref/validateattributes.html

I hope this helps!

[Nilay Modi]

How can I do this inside the arguments block?

arguments
    id (1,1) {mustBeNumeric, mustBePositive, mustBeInteger, mustBeNonempty}
    position (1,3) double {mustBeVector, mustBeNonempty, validatePositionArgument(position)}         
end
function validatePositionArgument(position)
    % Throws an error if the input 'position' is not a vector or if it's
    % length is not equal to 3.
    if ~isvector(position) || length(position) ~= 3
        error('Position must be a 1x3 vector.');
    end
end

Here, inside the validatePositionArgument function, the position argument is already converted to [20, 20, 20]. Your solution doesn't use the argments block. Is it not possible to do this with using arguments block? Thanks.