QtConcurrent: Introduce runWithPromise()

The differences to run() method:
1. The passed function should have additional
   argument QPromise<T> &, declared as a first argument.
2. The return value of the function must be void.
   Result reporting should be done through
   passed QPromise<T> &promise argument.
3. By default, runWithPromise() doesn't support functors
   with overloaded operator()().
   In case of overloaded functors the user
   needs to explicitly specify the result type
   as a template parameter passed to runWithPromise,
   like:

   struct Functor {
       void operator()(QPromise<int> &) { }
       void operator()(QPromise<double> &) { }
   };

   Functor f;

   runWithPromise<double>(f); // this will select the 2nd overload

Task-number: QTBUG-84702
Change-Id: Ie40d466938d316fc46eb7690e6ae0ce1c6c6d649
Reviewed-by: Sona Kurazyan <sona.kurazyan@qt.io>

2 files changed, 11 insertions, 0 deletions

diff --git a/src/corelib/thread/qpromise.h b/src/corelib/thread/qpromise.h
index 32aaa202f5..59c31de212 100644
--- a/src/corelib/thread/qpromise.h
+++ b/src/corelib/thread/qpromise.h
@@ -63,6 +63,7 @@ public:
     {
         other.d = QFutureInterface<T>();
     }
+    QPromise(QFutureInterface<T> &other) : d(other) {}
     QPromise& operator=(QPromise<T> &&other)
     {
         QPromise<T> tmp(std::move(other));
diff --git a/src/corelib/thread/qpromise.qdoc b/src/corelib/thread/qpromise.qdoc
index b404732a9e..9c7925da95 100644
--- a/src/corelib/thread/qpromise.qdoc
+++ b/src/corelib/thread/qpromise.qdoc
@@ -78,6 +78,16 @@
     \sa operator=()
 */
 
+/*! \fn template <typename T> QPromise<T>::QPromise(QFutureInterface<T> &other)
+
+    \internal
+    Constructs a QPromise with a passed QFutureInterface \a other.
+    Used internally for QtConcurrent::runWithPromise.
+
+    \sa operator=()
+*/
+
+
 /*! \fn template <typename T> QPromise<T> &QPromise<T>::operator=(QPromise<T> &&other)
 
     Move assigns \a other to this promise and returns a reference to this