Arguments function: Name-value arguments in default values

I am currently using Matlabs argument validation functionality (arguments) to validation an input struct (via conversion to name-value pair). I was wondering if there is any way to set the default value for name-argument pair as the value from a different name-value pair as below. Ideally this would set the default value of <>.B to be equal to <>.A if the value is not provided.

function my_func(nameValueInputStruct)
    arguments
        nameValueInputStruct.A double = 1
        nameValueInputStruct.B double = nameValueInputStruct.A
    end
...
end

Matlab throws the error when I try to do this, but was hoping that there is an available work-around. It is important that the input is a name-value pair struct. Thank you.

Use of name-value arguments in default values is not supported.

Answer 1

[Shivam Malviya]

Hi Austin,

I see that you are interested in utilizing the "A" name-value pair argument to assign a default value for the "B" name-value pair argument inside the function argument validation block. However, I regret to inform you that this feature is currently unsupported.

To work around this issue, please note that if a value is not provided for a specific name-value pair argument, it will not appear as a field in the name-value pair argument variable. With this in mind, I have created a function which is attached below for your reference and to help you understand this concept better.

function my_func(nameValueInputStruct)
    % Argument validation
    arguments
        nameValueInputStruct.A double = 1
        nameValueInputStruct.B double
    end

    % Call a helper function to parse the input struct
    parseNameValueInputStruct(nameValueInputStruct)
end

function parseNameValueInputStruct(nameValueInputStruct)
%parseNameValueInputStruct Parse the nameValueInputStruct and modify it 
%   accordingly

    % If value for argument "B" is not provided
    if ~isfield(nameValueInputStruct, "B")
        % Set the value of "B" equal to the value of "A"
        nameValueInputStruct.B = nameValueInputStruct.A;
    end
end

Please refer to the following links for a better understanding;

• https://in.mathworks.com/help/matlab/ref/isfield.html
• https://in.mathworks.com/help/matlab/ref/arguments.html

Best regards,

Shivam Malviya

Answer 2

[Markus Leuthold]

Same with this code, which I expect to work, but it fails with the same error message

arguments
    opts.A = mustBeMember(opts.A, ["x" "y"])
end