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Update the porting guide for QFuture

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Document the source compatibility breaks introduced by the recent
changes (ff0ba7e2d7b91fd5809cb314935a1ca1a436f6c9 and
30a1683f65fa0d01eceb7e1293abc84108d76e7f) in the porting guide.

Task-number: QTBUG-87096
Change-Id: I5b725c863b1077d59074d4bd17a4456e3d87918c
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>
This commit is contained in:
Sona Kurazyan 2020-11-02 11:06:26 +01:00
parent 75d32a195a
commit 3b8d37b1f0
1 changed files with 40 additions and 4 deletions
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src/corelib/doc/src/qt6-changes.qdoc
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@ -395,11 +395,47 @@
\section1 QFuture and Related Classes \section1 QFuture and Related Classes
\section2 QFuture and QFutureWatcher \section2 QFuture
In Qt 6, there are no changes that introduce source compatibility breaks To avoid unintended usage of QFuture, there were some changes to
in code that was using QFuture and QFutureWatcher classes. However there QFuture API in Qt 6, which may introduce source compatibility breaks.
were some improvements which caused the following behavioral changes:
\section3 Implicit conversions between QFuture and other types
Conversion of \c QFuture<T> to \c T has been disabled. The casting
operator was calling QFuture::result(), which may lead to undefined
behavior if the user has moved the results from QFuture via
QFuture::takeResult() before trying to do the conversion. Use
QFuture::result() or QFuture::takeResult() methods explicitly,
where you need to convert \c QFuture<T> to \c T.
The implicit conversion from \c QFuture<T> to \c QFuture<void> has
been also disabled. If you really intend to do the conversion, use the
explicit \c {QFuture<void>(const QFuture<T> &)} constructor:
\code
QFuture<int> future = ...
QFuture<void> voidFuture = QFuture<void>(future);
\endcode
\section3 Equality operators
The equality operators of QFuture have been removed. They were comparing
the underlying d-pointers instead of comparing the results, which is not
what users might expect. If you need to compare QFuture objects, use
\c QFuture::result() or \c QFuture::takeResult() methods. For example:
\code
QFuture<int> future1 = ...;
QFuture<int> future2 = ...;
if (future1.result() == future2.result())
// ...
\endcode
\section2 Behavioral Changes to QFuture and QFutureWatcher
In Qt 6, there were some improvements to QFuture and QFutureWatcher which
caused the following behavioral changes:
\list \list