[Development] implicit sharing and iterators in qt containers

[Mandeep Sandhu]

Hi All,

I recently stumbled upon an issue where using iterators of a QLinkedList,
altered the "copy" of another QLinkedList.

On reading the iterator docs, I came across this limitation of Qt
containers with implicit sharing:
http://doc.qt.io/qt-5/containers.html#implicit-sharing-iterator-problem

Basically this article advises against making copies of containers which
have active iterators on them.

I've written a Qt based "ordered map" which uses a QLinkedList for
maintaining order of keys (https://github.com/mandeepsandhu/qt-ordered-map).
However, due to the issue with implicit sharing & iterators, it's not
possible for a trivial assignment operator & copy c'tor. Is there any way
around it other than making a item-by-item copy of the linked list?

Thanks,
-mandeep
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