For the record, this was a perfectly good question. The QAbstractItemModel::createIndex() docs do not state that it embeds a model pointer into the index it creates, nor do the QModelIndex docs mention the private constructor that makes it possible.

This makes QModelIndex::parent() look suspicious if you happen to be troubleshooting a problem. If you want to be sure your model is implemented correctly, you have to put aside the docs and dig up the inline function definitions in qabstractitemmodel.h.

Of course I'll cast my -1 vote as well.

I'll add to point 1:

If the data contained in the model is all of basic types or implicitly shared types then it's possible to already use the current framework without ever triggering any expensive* copy

, to point 2:

There's no clarity on how to support different types in different roles would we need an additional template argument for each used role beyond Qt::UserRole? is so the problems above grow exponentially with the roles

And to point 3:

No possible implementation for a reliable dataChanged emission if model internals are exposed directly

*expensive = a copy that implies more that a:

memcpy of less than 65bits and an increase/decrease of a numeric reference counter