Bug: class field modified by reference

There is a major bug in Matlab in which the field of a class is modified when passed as an function argument but not requested as an output if the calling function modifies the value internally. In the minimal example below: b.value is not the same before and after calling test.

b.value = 10;
b.value,
a = test(b);
b.value

function a = test(b)
    a=1; b=b.value*10;
end

[Walter Roberson]

I am not seeing anything when I test your code in R2018a.

If b was being modified by the code you post, then it would no longer be a struct (because you are writing over all of b), and b.value would then be a failure.

Your question talks about "field of a class", but your demonstration involves a struct rather than a class.

[Antonio Mei]

Right, it only happens for when b is defined via classdef.

[Walter Roberson]

Please post actual example including classdef

Answer 1

[Steven Lord]

I tried this with a very simple class and it worked as I expected.

It sounds to me like b is an instance of a handle class. If that's the case, the behavior you described is correct as described in the "Handle Objects Modified in Functions" section on that documentation page (assuming that in your test function you assigned into the value property of the b object rather than overwriting the variable inside the function.) See the attached example. I expect the last line printed when you run that code to be "ans = 100".

[Antonio Mei]

Thank you for clarifying. I actually had used the "dynamicprops" property. Do you know of a way to dynamically define properties without recursing to a handle subclass?