Forbid implicit conversions between QFuture and other types

- Remove the casting operator of QFuture<T> to T. It calls
  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.

- Disable implicit conversion of QFuture<T> to QFuture<void>, by making
  the constructor explicit. If the users really intend to do the
  conversion, they should do it explicitly.

[ChangeLog][Source-Incompatible Changes][QFuture] Implicit conversions
of QFuture<T> to T and to QFuture<void> have been disabled. Use
QFuture::result() or QFuture::takeResult() where you need to convert
QFuture<T> to T. Use the explicit QFuture<void>(const QFuture<T> &)
constructor to convert QFuture<T> to QFuture<void>.

Change-Id: I153d4137d36365b1611ac934fb3ac2eb667fdd6c
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
Reviewed-by: Jarek Kobus <jaroslaw.kobus@qt.io>

1 files changed, 1 insertions, 1 deletions

diff --git a/examples/qtconcurrent/wordcount/main.cpp b/examples/qtconcurrent/wordcount/main.cpp
index ae8542a761..f4de2886a8 100644
--- a/examples/qtconcurrent/wordcount/main.cpp
+++ b/examples/qtconcurrent/wordcount/main.cpp
@@ -157,7 +157,7 @@ int main(int argc, char** argv)
     {
         QElapsedTimer timer;
         timer.start();
-        WordCount total = mappedReduced(files, countWords, reduce);
+        WordCount total = mappedReduced(files, countWords, reduce).result();
         mapReduceTime = timer.elapsed();
         qDebug() << "MapReduce" << mapReduceTime;
     }