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Setup

Let's say I have some function that a number of arrays as an input and does something with them that requires the arrays to have compatible sizes (i.e., to have the same sizes after implicit singleton dimension expansion). I have written a function mustBeCompatibleSize that throws an error if it's arguments have incompatible sizes. This works as expected. It correctly points out which argument is causing the error to the user.

function multiArrayOperation1(Array1, Array2, Array3)
    arguments
        Array1;
        Array2 {mustBeCompatibleSize(Array1, Array2)};
        Array3 {mustBeCompatibleSize(Array1, Array2, Array3)};
    end
    % Do something with Array1, Array2, and Array3.
end

For example, calling multiArrayOperation1(ones(5, 1), ones(1, 5), ones(5, 6)) will result in MATLAB telling the user that the 3rd argument was not compatible with previous arguments.

Issue

The issue comes about when I want to make a function that accepts any number of input arrays, using the (Repeating) arguments block, like in the example below. This example does not work, as the argument validator passes only one element at a time into the mustBeCompatibleSize function, and thus no error is thrown.

function multiArrayOperation2(Arrays)
    arguments (Repeating)
        Arrays {mustBeCompatibleSize};
    end
    % Do something with Arrays.
end

For example, calling multiArrayOperation2(ones(5, 1), ones(1, 5), ones(5, 6)) does not result in an error being thrown.

Nonoptimal Solution

Of course, we can just call the validation function manually after the arguments block. However, this does not display to the user which argument is causing the error as it does in the first example, and doesn't really utilize the arguments block for validation.

function multiArrayOperation3(Arrays)
    arguments (Repeating)
        Arrays;
    end

    mustBeCompatibleSize(Arrays{:});

    % Do something with Arrays.
end

For example, calling multiArrayOperation3(ones(5, 1), ones(1, 5), ones(5, 6)) throws an error as it should, but the user is not informed which specific argument is causing the error.

Question

Is there a better solution to this issue? Hopefully, there is a way to implement something similar to the second example.

Matthew Dvorsky
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  • Welcome to the site, and nice question! I haven't used this form of argument validation, but from the documention it seems it is not designed to do what you want, i.e. having an `arguments` block of dynamic size. or being able to dynamically refer to previous arguments in the validation of each one – Luis Mendo Nov 07 '22 at 22:50
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    Can you do `function multiArrayOperation(Array1, OtherArrays)`, and then `Arrays {@(arr) mustBeCompatibleSize(Array1, arr)};`? Oh, I see the example you give, being compatible with the first array wouldn't be enough of a test. – Cris Luengo Nov 07 '22 at 23:43
  • Thanks for the comments. I'm guessing Luis is right, that this is probably not an intended feature of the arguments block. Cris, that's a clever idea except, as you noted, it won't always work when checking for compatible sizes. However, it could be useful if the function was checking for something like equally-sized arguments instead. – Matthew Dvorsky Nov 10 '22 at 20:52

0 Answers0