Given a QTaggedPointer, users may write
taggedPtr = {};
to mean "reset it". This is error-prone: due to overload resolution,
this actually ends up calling QTaggedPointer<T>::operator=(T *),
which changes the pointer but *not* the tag, and not the implicitly
declared QTaggedPointer<T>:operator=(const QTaggedPointer<T> &)
which would reset both pointer and tag.
Given the idiomatic usage of {} is indeed to perform a full reset (cf.
std::exchange(obj, {}), std::take, etc.), work around this by disabling
the operator= overload for pointers in case an initializer list is
passed. In other words, make `={}` fall back to the implicitly
declared overload.
Note, this breaks some usages, such as
taggedPtr = {rawPtr};
but at least we get a compile error for these, and they don't look
common at all.
[ChangeLog][QtCore][QTaggedPointer] The operator assignment
taking a raw pointer has been reimplemented in order to avoid
subtle issues when assigning `{}` to a QTaggedPointer. This will
cause code that assigns a braced-init-list to a QTaggedPointer object
to stop compiling (for instance, `tagPtr = {ptr}` is now ill-formed).
Change-Id: I5e572a9b0f119ddb2df17f1797934933dff2ba7b
Task-number: QTBUG-106070
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
42b66bd809