Reacting to values derived from ListModels

[Bob64]

Suppose I have a ListModel which, amongst other fields, contains a label.

ListModel {
    id: myModel
    ListElement { label: ..., ... }
}

(Though in my case, I am actually not defining ListElements inline but adding items programmatically.)

So I am happy with using this model in some sort of view where the individual fields of the model are used in the view, and everything updates nicely.

However, what if I want to derive a value from the whole model? The case I have in mind is a maximum label length which I need to use in my UI. That maximum needs to be updated when the model updates and I would like to do it declaratively:

MyComponent {
    propertyThatDependsOnMaxLabelLength: ???
    ...
}

For example, would something like this work?

MyComponent {
    function calcMaxLabelLength(model) { ... }
    propertyThatDependsOnMaxLabelLength: calcMaxLabelLength(myModel)
    ...
}

i.e., would the function reliably be reevaluated whenever there is any change to the model?

I know I could write a C++ model and I could simply expose an additional property from that. This might be the best way in terms of efficiency but it seems like overkill for a case where a simple ListModel is otherwise sufficient.

[Bob64]

To partially answer my own question: based on a small test app, it certainly seems that the sort of function that I described does in practice get called whenever there is a change to the model.

Part of me thinks this maybe is obvious based on how things tend to work in QML but I would still feel happier to see it in black and white somewhere.