Make QPointer<T> constructible from QPointer<X>

QWeakPointer can do the same, so there's no reason to not allow it for
QPointer.

[ChangeLog][QtCore][QPointer] QPointer<T> can now be (move- and
copy-)constructed from QPointer<X>.

Fixes: QTBUG-112464
Change-Id: I77cf5d39974bf2b3ec849b4afc33e286e864821e
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>

1 files changed, 10 insertions, 0 deletions

diff --git a/src/corelib/kernel/qpointer.h b/src/corelib/kernel/qpointer.h
index 2c82441164..ada4445d43 100644
--- a/src/corelib/kernel/qpointer.h
+++ b/src/corelib/kernel/qpointer.h
@@ -18,6 +18,11 @@ class QPointer
 {
     static_assert(!std::is_pointer<T>::value, "QPointer's template type must not be a pointer type");
 
+    template <typename X>
+    using if_convertible = std::enable_if_t<std::is_convertible_v<X*, T*>, bool>;
+    template <typename X>
+    friend class QPointer;
+
     using QObjectType =
         typename std::conditional<std::is_const<T>::value, const QObject, QObject>::type;
     QWeakPointer<QObjectType> wp;
@@ -27,6 +32,11 @@ public:
     // compiler-generated copy/move ctor/assignment operators are fine!
     // compiler-generated dtor is fine!
 
+    template <typename X, if_convertible<X> = true>
+    QPointer(QPointer<X> &&other) noexcept : wp(std::move(other.wp)) {}
+    template <typename X, if_convertible<X> = true>
+    QPointer(const QPointer<X> &other) noexcept : wp(other.wp) {}
+
 #ifdef Q_QDOC
     // Stop qdoc from complaining about missing function
     ~QPointer();