If a QRangeModel represents a C++ range, then the C++ range must no longer be modified directly, as clients of the model won't be notified about data or structural changes. Ignoring this (documented) warning might end up with views not presenting the data correctly, or even result in crashes as the model cannot update QPersistentModelIndex instances. Modifying the range through the QAbstractItemModel API is ok, but clumsy, as it requires dealing with QModelIndex and QVariant for basic operations. QRangeModelAdapter provides an easy, type safe, and data-structure aware API for reading and also modifying a range that a QRangeModel operates on. This includes an interator API for rows, and - unless the range is a list - columns. Dereferencing row iterators yields a row reference type from which a row can be accessed for reading, or that a new row can be assigned to. Dereferencing a const column iterator yields an item; dereferencing a mutable column iterator yields a reference type that a new item value can be assigned to. Since QRangeModel itself is not a template class (so we don't know the type of the range anymore once it has been created), we have to create the adapter from the range (and optional protocol), which then implicitly creates the model. Constructing the adapter implicitly constructs the model, which is owned by the adapter. QRangeModelAdapter is a value type, using std::shared_ptr for the model so that all copies of the adapter operate on the same model. To be able to set entire multi-role objects as items, introduce a new Qt::ItemDataRole enum value, Qt::RangeModelAdapterRole. This is very similar to Qt::RangeModelDataRole, but QML has specific requirements that QRangeModelAdapter doesn't have, and we want to pass items back and forth without modifying their value category - ie. an item that is a shared_ptr<Object> is not useful for QML (which needs an Object *), but a C++ user expects to get a shared_ptr<Object> from a call to at(), and also expects to be able to set such an item. The code has room for de-duplicating some logic in follow-up commits. [ChangeLog][Core] Added QRangeModelAdapter for C++-style access to a range used in a QRangeModel, while implementing QAbstractItemModel protocol. Change-Id: I3f2f94cb51b850100590fbe2c9a7c9dabbec59bd Reviewed-by: Artem Dyomin <artem.dyomin@qt.io>