An update on this from my side:

My initial approach wasn't flawless, as @VRonin pointed out, because QAbstractItemModel::columnCount didn't return the appropriate values. I've fixed this, by not immediately passing the new count after inserting the elements to a list, of which the size was used, but instead have the model save exactly how many categories it currently accounts for, so the connection looks like this:

connect(item_registry.get(), &item_registry::category_added, [this](int position, QSharedPointer<category>) { beginInsertColumns(QModelIndex{}, position, position); _current_category_count++; endInsertColumns(); });

and likewise columnCount:

int item_model::columnCount(QModelIndex const&) const { if(!_register) { qCritical() << "Item-model didn't have a register"; return 0; } return 1 /* name */ + _current_category_count; }

QListView {outline: none;}

If you mean outside of answering question here in forum, then no thank you. :)

I am curious then if you would like to clarify related development topics.

Do you know any higher level tools which can display structural differences between standard item models in a clear way? Have you got any experiences with “diff views” in this software area?