The idea is to store a concatenable in a QStringBuilder object by value
or by reference, depending on how it was originally passed into the
concatenation operator. So if it was passed by r-value, we treat it as
a temporary object and hold it by value (and use move-semantic if
available), otherwise we hold it by reference (as before).
To achieve this we first change concatenation operators '%' and '+'
to take their arguments by universal reference. Next we instantiate
QStringBuilder object with deduced types of the arguments, which will
be a "value type" or a "reference type" according to "universal
reference deduction rules".
Further we use perfect forwarding to pass arguments to QStringBuilder's
constructor. Thus arguments, initially passed by r-value reference
and which are move-constructible, will be "moved" to corresponding
QStringBuilder member variables.
So, to summarize:
1. Arguments passed by l-value reference - stored in QStringBuilder
object by reference (as before).
2. Temporary objects passed by r-value reference - stored in
QStringBuilder object by value. If a type is move-constructible
(QSting, QByteArray, etc), the object will be "moved" accordingly.
Special thanks to Giuseppe D'Angelo for the tests.
Fixes: QTBUG-99291
Fixes: QTBUG-87603
Fixes: QTBUG-47066
Task-number: QTBUG-74873
Task-number: QTBUG-103090
Task-number: QTBUG-104354
Change-Id: I64f417be0de0815ec5ae7e35a1cc6cef6d887933
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Vladimir Belyavsky <belyavskyv@gmail.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Marc Mutz <marc.mutz@qt.io>
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