Include variable value when throwing exception

I have a function that throws a specific exception, and a try/catch block in a top-level function that handles it. I want to pass along the value of some variables in addition to the error message for debugging purposes. Typically cell array, string array or numerical matrix.

I'm guessing I would have to create a custom exception class for this?

Follow-up: Why is the default MException so restrictive? Is error handling like I described a bad practice?

[Marc Youcef]

I was looking for same thing as well. I hav objects being instantiated in a loop and when it fails I would like to know which index of instantiation failed.

[Daniel]

You can subclass MException and add any custom properties to do exactly that. See my answer.

Answer 1

[Daniel]

To add custom data to an exception, subclass MException and add custom properties.

classdef MyException < MException
    properties
        Data
    end
end

Then, in code, use your custom property as so:

try
    ex = MyException('root:cause', 'error message');
    ex.Data = 1234;
    ex.throw()
catch ME
    disp(ME.Data)
end

Answer 2

[Steven Lord]

Why not just build up the appropriate string containing the message with the information you want it to include then call error to throw an error with that message?

expectsOnlyScalar(pi)

Good, you passed in the scalar value 3.1416

expectsOnlyScalar(1:10)

Error using solution>expectsOnlyScalar (line 9)
I expected a scalar value but instead you passed in an array of size [1 10]!

function expectsOnlyScalar(x)
if isscalar(x)
    disp("Good, you passed in the scalar value " + x)
else
    msg = "I expected a scalar value but instead " + ...
          "you passed in an array of size " + mat2str(size(x)) + "!";
    error(msg)
end
end