qt - How to avoid objects copying during passing from C++ to QML and again to C++? -


i try load qimage c++ qml. created subclass of qquickpainteditem in load qimage(casted qvariant) using slot(that means use qml in case transfer). have 1 issue: pass qimage value, , know can't pass arguments qml c++ using references , pointers.

so, whether there trick allows avoid objects copying during passing c++ qml , again c++?

the "trick" built in qt: many other classes contain data, qimage uses implicit data sharing aka copy-on-write/cow, quote qt5 docs:

qimage objects can passed around value since qimage class uses implicit data sharing.

link in docs provides more details means in context of qt, in short actual qimage instance small , cheap pass around value. pointer shared data reference count. when instance modified, detached (deep copy taken) first if reference count greater 1, when not modifying, it's copying around pointer.


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