Add support for initializing QSharedPointer from nullptr

std::shared_ptr supports it. To resolve an ambiguous overload when a
literal 0 is passed as a parameter, the normal constructors needed to be
made a template, like std::shared_ptr.

Task-number: QTBUG-52569
Change-Id: Id75834dab9ed466e94c7ffff14451417892d2148
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>

3 files changed, 32 insertions, 9 deletions

diff --git a/src/corelib/tools/qsharedpointer.cpp b/src/corelib/tools/qsharedpointer.cpp
index d03e3129aa..f420c6237b 100644
--- a/src/corelib/tools/qsharedpointer.cpp
+++ b/src/corelib/tools/qsharedpointer.cpp
@@ -442,7 +442,7 @@
 */
 
 /*!
-    \fn QSharedPointer::QSharedPointer(T *ptr)
+    \fn QSharedPointer::QSharedPointer(X *ptr)
 
     Creates a QSharedPointer that points to \a ptr. The pointer \a ptr
     becomes managed by this QSharedPointer and must not be passed to
@@ -450,7 +450,7 @@
 */
 
 /*!
-    \fn QSharedPointer::QSharedPointer(T *ptr, Deleter deleter)
+    \fn QSharedPointer::QSharedPointer(X *ptr, Deleter deleter)
 
     Creates a QSharedPointer that points to \a ptr. The pointer \a ptr
     becomes managed by this QSharedPointer and must not be passed to
@@ -487,6 +487,22 @@
 */
 
 /*!
+    \fn QSharedPointer::QSharedPointer(std::nullptr_t)
+    \since 5.8
+
+    Creates a QSharedPointer that is null. This is equivalent to the
+    QSharedPointer default constructor.
+*/
+
+/*!
+    \fn QSharedPointer::QSharedPointer(std::nullptr_t, Deleter)
+    \since 5.8
+
+    Creates a QSharedPointer that is null. This is equivalent to the
+    QSharedPointer default constructor.
+*/
+
+/*!
     \fn QSharedPointer::QSharedPointer(const QSharedPointer<T> &other)
 
     Creates a QSharedPointer object that shares \a other's pointer.
diff --git a/src/corelib/tools/qsharedpointer.h b/src/corelib/tools/qsharedpointer.h
index 6742a66939..3e05bf1ece 100644
--- a/src/corelib/tools/qsharedpointer.h
+++ b/src/corelib/tools/qsharedpointer.h
@@ -67,9 +67,10 @@ public:
 
     // constructors
     QSharedPointer();
-    explicit QSharedPointer(T *ptr);
-    template<typename Deleter>
-    QSharedPointer(T *ptr, Deleter d);
+    template <typename X> explicit QSharedPointer(X *ptr);
+    template <typename X, typename Deleter> QSharedPointer(X *ptr, Deleter d);
+    QSharedPointer(std::nullptr_t);
+    template <typename Deleter> QSharedPointer(std::nullptr_t, Deleter d);
     QSharedPointer(const QSharedPointer<T> &other);
     QSharedPointer(const QWeakPointer<T> &other);
 
diff --git a/src/corelib/tools/qsharedpointer_impl.h b/src/corelib/tools/qsharedpointer_impl.h
index 6a5c8f4fe5..b9b29e926d 100644
--- a/src/corelib/tools/qsharedpointer_impl.h
+++ b/src/corelib/tools/qsharedpointer_impl.h
@@ -313,16 +313,22 @@ public:
     inline T &operator*() const { return *data(); }
     inline T *operator->() const { return data(); }
 
-    QSharedPointer() Q_DECL_NOTHROW : value(Q_NULLPTR), d(Q_NULLPTR) {}
+    Q_DECL_CONSTEXPR QSharedPointer() Q_DECL_NOTHROW : value(nullptr), d(nullptr) { }
     ~QSharedPointer() { deref(); }
 
-    inline explicit QSharedPointer(T *ptr) : value(ptr) // noexcept
+    Q_DECL_CONSTEXPR QSharedPointer(std::nullptr_t) Q_DECL_NOTHROW : value(nullptr), d(nullptr) { }
+
+    template <class X>
+    inline explicit QSharedPointer(X *ptr) : value(ptr) // noexcept
     { internalConstruct(ptr, QtSharedPointer::NormalDeleter()); }
 
-    template <typename Deleter>
-    inline QSharedPointer(T *ptr, Deleter deleter) : value(ptr) // throws
+    template <class X, typename Deleter>
+    inline QSharedPointer(X *ptr, Deleter deleter) : value(ptr) // throws
     { internalConstruct(ptr, deleter); }
 
+    template <typename Deleter>
+    QSharedPointer(std::nullptr_t, Deleter) : value(nullptr), d(nullptr) { }
+
     QSharedPointer(const QSharedPointer &other) Q_DECL_NOTHROW : value(other.value), d(other.d)
     { if (d) ref(); }
     QSharedPointer &operator=(const QSharedPointer &other) Q_DECL_NOTHROW