Centralize the implementation of move assignment operators

At the moment we have two main strategies for dealing with move
assignment in Qt:

1) move-and-swap, used by "containers" (in the broad sense): containers,
but also smart pointers and similar classes that can hold user-defined
types;

2) pure swap, used by containers that hold only memory (e.g. QString,
QByteArray, ...) as well as most implicitly shared datatypes.

Given the fact that a move assignment operator's code is just
boilerplate (whether it's move-and-swap or pure swap), provide two
_strictly internal_ macros to help write them, and apply the macros
across corelib and gui, porting away from the hand-rolled
implementations.

The rule of thumb when porting to the new macros is:

* Try to stick to the existing code behavior, unless broken

* if changing, then follow this checklist:

  * if the class does not have a move constructor => pure swap
    (but consider ADDING a move constructor, if possible!)

  * if the class does have a move constructor, try to follow the
     criteria above, namely:

    * if the class holds only memory, pure swap;

    * if the class may hold anything else but memory (file handles,
      etc.), then move and swap.

Noteworthy details:

* some operators planned to be removed in Qt 6 were not ported;

* as drive-by, some move constructors were simplified to be using
qExchange(); others were outright broken and got fixed;

* some contained some more interesting code and were not touched.

Change-Id: Idaab3489247dcbabb6df3fa1e5286b69e1d372e9
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>

src/corelib/global/qglobal.h

@@ -431,6 +431,51 @@ Q_DECL_UNUSED constexpr Deprecated_t Deprecated = {};
     Q_DISABLE_COPY(Class) \
     Q_DISABLE_MOVE(Class)
 
+/*
+    Implementing a move assignment operator using an established
+    technique (move-and-swap, pure swap) is just boilerplate.
+    Here's a couple of *private* macros for convenience.
+
+    To know which one to use:
+
+    * if you don't have a move constructor (*) => use pure swap;
+    * if you have a move constructor, then
+      * if your class holds just memory (no file handles, no user-defined
+        datatypes, etc.) => use pure swap;
+      * use move and swap.
+
+    The preference should always go for the move-and-swap one, as it
+    will deterministically destroy the data previously held in *this,
+    and not "dump" it in the moved-from object (which may then be alive
+    for longer).
+
+    The requirement for either macro is the presence of a member swap(),
+    which any value class that defines its own special member functions
+    should have anyhow.
+
+    (*) Many value classes in Qt do not have move constructors; mostly,
+    the implicitly shared classes using QSharedDataPointer and friends.
+    The reason is mostly historical: those classes require either an
+    out-of-line move constructor, which we could not provide before we
+    made C++11 mandatory (and that we don't like anyhow), or
+    an out-of-line dtor for the Q(E)DSP<Private> member (cf. QPixmap).
+
+    If you can however add a move constructor to a class lacking it,
+    consider doing so, then reevaluate which macro to choose.
+*/
+#define QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_MOVE_AND_SWAP(Class) \
+    Class &operator=(Class &&other) noexcept { \
+        Class moved(std::move(other)); \
+        swap(moved); \
+        return *this; \
+    }
+
+#define QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(Class) \
+    Class &operator=(Class &&other) noexcept { \
+        swap(other); \
+        return *this; \
+    }
+
 /*
    No, this is not an evil backdoor. QT_BUILD_INTERNAL just exports more symbols
    for Qt's internal unit tests. If you want slower loading times and more

src/corelib/io/qdebug.h

@@ -102,8 +102,7 @@ public:
     QDebug(const QDebug &o) : stream(o.stream) { ++stream->ref; }
     QDebug(QDebug &&other) noexcept : stream{qExchange(other.stream, nullptr)} {}
     inline QDebug &operator=(const QDebug &other);
-    QDebug &operator=(QDebug &&other) noexcept
-    { QDebug{std::move(other)}.swap(*this); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_MOVE_AND_SWAP(QDebug)
     ~QDebug();
     inline void swap(QDebug &other) noexcept { qSwap(stream, other.stream); }
 

src/corelib/io/qdir.h

@@ -121,7 +121,7 @@ public:
     ~QDir();
 
     QDir &operator=(const QDir &);
-    QDir &operator=(QDir &&other) noexcept { swap(other); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QDir)
 
     void swap(QDir &other) noexcept
     { qSwap(d_ptr, other.d_ptr); }

src/corelib/io/qfileinfo.h

@@ -79,7 +79,7 @@ public:
     ~QFileInfo();
 
     QFileInfo &operator=(const QFileInfo &fileinfo);
-    QFileInfo &operator=(QFileInfo &&other) noexcept { swap(other); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QFileInfo)
 
     void swap(QFileInfo &other) noexcept
     { qSwap(d_ptr, other.d_ptr); }

src/corelib/io/qprocess.h

@@ -68,7 +68,7 @@ public:
     QProcessEnvironment();
     QProcessEnvironment(const QProcessEnvironment &other);
     ~QProcessEnvironment();
-    QProcessEnvironment &operator=(QProcessEnvironment && other) noexcept { swap(other); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QProcessEnvironment)
     QProcessEnvironment &operator=(const QProcessEnvironment &other);
 
     void swap(QProcessEnvironment &other) noexcept { qSwap(d, other.d); }

src/corelib/io/qstorageinfo.h

@@ -62,7 +62,7 @@ public:
     ~QStorageInfo();
 
     QStorageInfo &operator=(const QStorageInfo &other);
-    QStorageInfo &operator=(QStorageInfo &&other) noexcept { swap(other); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QStorageInfo)
 
     inline void swap(QStorageInfo &other) noexcept
     { qSwap(d, other.d); }

src/corelib/io/qurl.h

@@ -184,8 +184,7 @@ public:
 #endif
     QUrl(QUrl &&other) noexcept : d(other.d)
     { other.d = nullptr; }
-    inline QUrl &operator=(QUrl &&other) noexcept
-    { qSwap(d, other.d); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QUrl)
     ~QUrl();
 
     inline void swap(QUrl &other) noexcept { qSwap(d, other.d); }

src/corelib/io/qurlquery.h

@@ -67,7 +67,7 @@ public:
 
     QUrlQuery(const QUrlQuery &other);
     QUrlQuery &operator=(const QUrlQuery &other);
-    QUrlQuery &operator=(QUrlQuery &&other) noexcept { swap(other); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QUrlQuery)
     ~QUrlQuery();
 
     bool operator==(const QUrlQuery &other) const;

src/corelib/itemmodels/qabstractitemmodel.h

@@ -220,9 +220,8 @@ public:
     { return !operator==(other); }
     QPersistentModelIndex &operator=(const QPersistentModelIndex &other);
     inline QPersistentModelIndex(QPersistentModelIndex &&other) noexcept
-        : d(other.d) { other.d = nullptr; }
-    inline QPersistentModelIndex &operator=(QPersistentModelIndex &&other) noexcept
-    { qSwap(d, other.d); return *this; }
+        : d(qExchange(other.d, nullptr)) {}
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QPersistentModelIndex)
     inline void swap(QPersistentModelIndex &other) noexcept { qSwap(d, other.d); }
     bool operator==(const QModelIndex &other) const;
     bool operator!=(const QModelIndex &other) const;

src/corelib/kernel/qbasictimer.h

@@ -61,11 +61,7 @@ public:
         : id{qExchange(other.id, 0)}
     {}
 
-    QBasicTimer& operator=(QBasicTimer &&other) noexcept
-    {
-        QBasicTimer{std::move(other)}.swap(*this);
-        return *this;
-    }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_MOVE_AND_SWAP(QBasicTimer)
 
     void swap(QBasicTimer &other) noexcept { qSwap(id, other.id); }
 

src/corelib/kernel/qcore_mac_p.h

@@ -260,21 +260,12 @@ public:
     QAppleLogActivity(os_activity_t activity) : activity(activity) {}
     ~QAppleLogActivity() { if (activity) leave(); }
 
-    QAppleLogActivity(const QAppleLogActivity &) = delete;
-    QAppleLogActivity& operator=(const QAppleLogActivity &) = delete;
+    Q_DISABLE_COPY(QAppleLogActivity)
 
     QAppleLogActivity(QAppleLogActivity&& other)
-        : activity(other.activity), state(other.state) { other.activity = nullptr; }
+        : activity(qExchange(other.activity, nullptr)), state(other.state) {}
 
-    QAppleLogActivity& operator=(QAppleLogActivity &&other)
-    {
-        if (this != &other) {
-            activity = other.activity;
-            state = other.state;
-            other.activity = nullptr;
-        }
-        return *this;
-    }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_MOVE_AND_SWAP(QAppleLogActivity)
 
     QAppleLogActivity&& enter()
     {
@@ -343,18 +334,14 @@ public:
 #endif
 
     QMacNotificationObserver(const QMacNotificationObserver& other) = delete;
-    QMacNotificationObserver(QMacNotificationObserver&& other) : observer(other.observer) {
-        other.observer = nullptr;
-    }
+    QMacNotificationObserver(QMacNotificationObserver&& other) : observer(qExchange(other.observer, nullptr)) {}
 
     QMacNotificationObserver &operator=(const QMacNotificationObserver& other) = delete;
-    QMacNotificationObserver &operator=(QMacNotificationObserver&& other) {
-        if (this != &other) {
-            remove();
-            observer = other.observer;
-            other.observer = nullptr;
-        }
-        return *this;
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_MOVE_AND_SWAP(QMacNotificationObserver)
+
+    void swap(QMacNotificationObserver &other) noexcept
+    {
+        qSwap(observer, other.observer);
     }
 
     void remove();
@@ -397,11 +384,7 @@ public:
         return *this;
     }
 
-    QMacKeyValueObserver &operator=(QMacKeyValueObserver &&other) {
-        QMacKeyValueObserver tmp(std::move(other));
-        swap(tmp, *this);
-        return *this;
-    }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_MOVE_AND_SWAP(QMacKeyValueObserver)
 
     void removeObserver();
 

src/corelib/kernel/qmetaobject.cpp

@@ -1597,6 +1597,14 @@ bool QMetaObject::invokeMethodImpl(QObject *object, QtPrivate::QSlotObjectBase *
     that \a o was pointing to.
 */
 
+/*!
+    \fn QMetaObject::Connection::swap(Connection &other)
+    \since 5.15
+
+    Swaps this Connection instance with \a other. This operation is very fast
+    and never fails.
+*/
+
 /*!
     \class QMetaMethod
     \inmodule QtCore

src/corelib/kernel/qobjectdefs.h

@@ -459,11 +459,16 @@ public:
     operator RestrictedBool() const { return d_ptr && isConnected_helper() ? &Connection::d_ptr : nullptr; }
 #endif
 
-    Connection(Connection &&o) noexcept : d_ptr(o.d_ptr) { o.d_ptr = nullptr; }
-    Connection &operator=(Connection &&other) noexcept
-    { qSwap(d_ptr, other.d_ptr); return *this; }
+    Connection(Connection &&o) noexcept : d_ptr(qExchange(o.d_ptr, nullptr)) {}
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(Connection)
+    void swap(Connection &o) noexcept { qSwap(d_ptr, o.d_ptr); }
 };
 
+inline void swap(QMetaObject::Connection &lhs, QMetaObject::Connection &rhs) noexcept
+{
+    lhs.swap(rhs);
+}
+
 inline const QMetaObject *QMetaObject::superClass() const
 { return d.superdata; }
 

src/corelib/kernel/qvariant.h

@@ -234,8 +234,7 @@ class Q_CORE_EXPORT QVariant
     QVariant& operator=(const QVariant &other);
     inline QVariant(QVariant &&other) noexcept : d(other.d)
     { other.d = Private(); }
-    inline QVariant &operator=(QVariant &&other) noexcept
-    { QVariant moved(std::move(other)); swap(moved); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_MOVE_AND_SWAP(QVariant)
 
     inline void swap(QVariant &other) noexcept { qSwap(d, other.d); }
 

src/corelib/kernel/qwinregistry_p.h

@@ -68,9 +68,9 @@ public:
                              REGSAM permissions = KEY_READ, REGSAM access = 0);
     ~QWinRegistryKey();
 
-    QWinRegistryKey(QWinRegistryKey &&other) noexcept { swap(other); }
-    QWinRegistryKey &operator=(QWinRegistryKey &&other) noexcept { swap(other); return *this; }
-
+    QWinRegistryKey(QWinRegistryKey &&other) noexcept
+        : m_key(qExchange(other.m_key, nullptr)) {}
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_MOVE_AND_SWAP(QWinRegistryKey)
     void swap(QWinRegistryKey &other) noexcept { qSwap(m_key, other.m_key); }
 
     bool isValid() const { return m_key != nullptr; }

src/corelib/mimetypes/qmimetype.h

@@ -78,7 +78,7 @@ public:
     QMimeType();
     QMimeType(const QMimeType &other);
     QMimeType &operator=(const QMimeType &other);
-    QMimeType &operator=(QMimeType &&other) noexcept { swap(other); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QMimeType)
     void swap(QMimeType &other) noexcept
     {
         qSwap(d, other.d);

src/corelib/serialization/qcborvalue.h

@@ -185,12 +185,7 @@ public:
         other.container = nullptr;
     }
     QCborValue &operator=(const QCborValue &other);
-    QCborValue &operator=(QCborValue &&other) noexcept
-    {
-        QCborValue tmp(std::move(other));
-        swap(tmp);
-        return *this;
-    }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_MOVE_AND_SWAP(QCborValue)
 
     void swap(QCborValue &other) noexcept
     {

src/corelib/text/qbytearray.h

@@ -170,8 +170,7 @@ public:
     QByteArray &operator=(const char *str);
     inline QByteArray(QByteArray && other) noexcept
     { qSwap(d, other.d); }
-    inline QByteArray &operator=(QByteArray &&other) noexcept
-    { qSwap(d, other.d); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QByteArray)
     inline void swap(QByteArray &other) noexcept
     { qSwap(d, other.d); }
 

src/corelib/text/qcollator.h

@@ -57,8 +57,7 @@ public:
     QCollatorSortKey(const QCollatorSortKey &other);
     ~QCollatorSortKey();
     QCollatorSortKey &operator=(const QCollatorSortKey &other);
-    inline QCollatorSortKey &operator=(QCollatorSortKey &&other) noexcept
-    { swap(other); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QCollatorSortKey)
     void swap(QCollatorSortKey &other) noexcept
     { d.swap(other.d); }
 
@@ -88,8 +87,7 @@ public:
     QCollator &operator=(const QCollator &);
     QCollator(QCollator &&other) noexcept
         : d(other.d) { other.d = nullptr; }
-    QCollator &operator=(QCollator &&other) noexcept
-    { swap(other); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_MOVE_AND_SWAP(QCollator)
 
     void swap(QCollator &other) noexcept
     { qSwap(d, other.d); }

src/corelib/text/qlocale.h

@@ -944,7 +944,7 @@ public:
     QLocale(Language language, Country country = AnyCountry);
     QLocale(Language language, Script script, Country country);
     QLocale(const QLocale &other);
-    QLocale &operator=(QLocale &&other) noexcept { swap(other); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QLocale)
     QLocale &operator=(const QLocale &other);
     ~QLocale();
 

src/corelib/text/qregularexpression.h

@@ -88,8 +88,7 @@ public:
     QRegularExpression(const QRegularExpression &re);
     ~QRegularExpression();
     QRegularExpression &operator=(const QRegularExpression &re);
-    QRegularExpression &operator=(QRegularExpression &&re) noexcept
-    { d.swap(re.d); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QRegularExpression)
 
     void swap(QRegularExpression &other) noexcept { d.swap(other.d); }
 

src/corelib/text/qstring.h

@@ -337,8 +337,7 @@ public:
     QString &operator=(QLatin1String latin1);
     inline QString(QString &&other) noexcept
     { qSwap(d, other.d); }
-    inline QString &operator=(QString &&other) noexcept
-    { qSwap(d, other.d); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QString)
     inline void swap(QString &other) noexcept { qSwap(d, other.d); }
     inline qsizetype size() const { return d.size; }
     inline qsizetype count() const { return d.size; }

src/corelib/thread/qsemaphore.h

@@ -83,8 +83,7 @@ public:
         : m_sem(sem), m_n(n) {}
     QSemaphoreReleaser(QSemaphoreReleaser &&other) noexcept
         : m_sem(other.cancel()), m_n(other.m_n) {}
-    QSemaphoreReleaser &operator=(QSemaphoreReleaser &&other) noexcept
-    { QSemaphoreReleaser moved(std::move(other)); swap(moved); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_MOVE_AND_SWAP(QSemaphoreReleaser)
 
     ~QSemaphoreReleaser()
     {

src/corelib/time/qdatetime.h

@@ -271,7 +271,7 @@ public:
     QDateTime(QDateTime &&other) noexcept;
     ~QDateTime();
 
-    QDateTime &operator=(QDateTime &&other) noexcept { swap(other); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QDateTime)
     QDateTime &operator=(const QDateTime &other) noexcept;
 
     void swap(QDateTime &other) noexcept { qSwap(d.d, other.d.d); }

src/corelib/time/qtimezone.h

@@ -99,7 +99,7 @@ public:
     ~QTimeZone();
 
     QTimeZone &operator=(const QTimeZone &other);
-    QTimeZone &operator=(QTimeZone &&other) noexcept { swap(other); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QTimeZone)
 
     void swap(QTimeZone &other) noexcept
     { d.swap(other.d); }

src/corelib/tools/qarraydatapointer.h

@@ -101,12 +101,7 @@ public:
         other.size = 0;
     }
 
-    QArrayDataPointer &operator=(QArrayDataPointer &&other) noexcept
-    {
-        QArrayDataPointer moved(std::move(other));
-        swap(moved);
-        return *this;
-    }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_MOVE_AND_SWAP(QArrayDataPointer)
 
     DataOps &operator*() noexcept
     {

src/corelib/tools/qbitarray.h

@@ -61,8 +61,7 @@ public:
     QBitArray(const QBitArray &other) : d(other.d) {}
     inline QBitArray &operator=(const QBitArray &other) { d = other.d; return *this; }
     inline QBitArray(QBitArray &&other) noexcept : d(std::move(other.d)) {}
-    inline QBitArray &operator=(QBitArray &&other) noexcept
-    { qSwap(d, other.d); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QBitArray)
 
     inline void swap(QBitArray &other) noexcept { qSwap(d, other.d); }
 

src/corelib/tools/qcommandlineoption.h

@@ -72,7 +72,7 @@ public:
     ~QCommandLineOption();
 
     QCommandLineOption &operator=(const QCommandLineOption &other);
-    QCommandLineOption &operator=(QCommandLineOption &&other) noexcept { swap(other); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QCommandLineOption)
 
     void swap(QCommandLineOption &other) noexcept
     { qSwap(d, other.d); }

src/corelib/tools/qcontiguouscache.h

@@ -94,8 +94,7 @@ public:
     inline bool isDetached() const { return d->ref.loadRelaxed() == 1; }
 
     QContiguousCache<T> &operator=(const QContiguousCache<T> &other);
-    inline QContiguousCache<T> &operator=(QContiguousCache<T> &&other) noexcept
-    { qSwap(d, other.d); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QContiguousCache)
     inline void swap(QContiguousCache<T> &other) noexcept { qSwap(d, other.d); }
 
     template <typename U = T>

src/corelib/tools/qeasingcurve.h

@@ -80,8 +80,7 @@ public:
     QEasingCurve &operator=(const QEasingCurve &other)
     { if ( this != &other ) { QEasingCurve copy(other); swap(copy); } return *this; }
     QEasingCurve(QEasingCurve &&other) noexcept : d_ptr(other.d_ptr) { other.d_ptr = nullptr; }
-    QEasingCurve &operator=(QEasingCurve &&other) noexcept
-    { qSwap(d_ptr, other.d_ptr); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QEasingCurve)
 
     void swap(QEasingCurve &other) noexcept { qSwap(d_ptr, other.d_ptr); }
 

src/corelib/tools/qhash.h

@@ -750,15 +750,7 @@ public:
         : d(std::exchange(other.d, nullptr))
     {
     }
-    QHash &operator=(QHash &&other) noexcept(std::is_nothrow_destructible<Node>::value)
-    {
-        if (d != other.d) {
-            if (d && !d->ref.deref())
-                delete d;
-            d = std::exchange(other.d, nullptr);
-        }
-        return *this;
-    }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_MOVE_AND_SWAP(QHash)
 #ifdef Q_QDOC
     template <typename InputIterator>
     QHash(InputIterator f, InputIterator l);

src/corelib/tools/qringbuffer_p.h

@@ -94,11 +94,7 @@ public:
     {
         other.headOffset = other.tailOffset = 0;
     }
-    inline QRingChunk &operator=(QRingChunk &&other) noexcept
-    {
-        swap(other);
-        return *this;
-    }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QRingChunk)
 
     inline void swap(QRingChunk &other) noexcept
     {

src/corelib/tools/qshareddata.h

@@ -111,13 +111,8 @@ public:
         }
         return *this;
     }
-    QSharedDataPointer(QSharedDataPointer &&o) noexcept : d(o.d) { o.d = nullptr; }
-    inline QSharedDataPointer<T> &operator=(QSharedDataPointer<T> &&other) noexcept
-    {
-        QSharedDataPointer moved(std::move(other));
-        swap(moved);
-        return *this;
-    }
+    QSharedDataPointer(QSharedDataPointer &&o) noexcept : d(qExchange(o.d, nullptr)) {}
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_MOVE_AND_SWAP(QSharedDataPointer)
 
     inline bool operator!() const { return !d; }
 
@@ -216,13 +211,8 @@ public:
         }
         return *this;
     }
-    inline QExplicitlySharedDataPointer(QExplicitlySharedDataPointer &&o) noexcept : d(o.d) { o.d = nullptr; }
-    inline QExplicitlySharedDataPointer<T> &operator=(QExplicitlySharedDataPointer<T> &&other) noexcept
-    {
-        QExplicitlySharedDataPointer moved(std::move(other));
-        swap(moved);
-        return *this;
-    }
+    inline QExplicitlySharedDataPointer(QExplicitlySharedDataPointer &&o) noexcept : d(qExchange(o.d, nullptr)) {}
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_MOVE_AND_SWAP(QExplicitlySharedDataPointer)
 
     inline bool operator!() const { return !d; }
 

src/corelib/tools/qsharedpointer_impl.h

@@ -333,12 +333,7 @@ public:
         other.d = nullptr;
         other.value = nullptr;
     }
-    QSharedPointer &operator=(QSharedPointer &&other) noexcept
-    {
-        QSharedPointer moved(std::move(other));
-        swap(moved);
-        return *this;
-    }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_MOVE_AND_SWAP(QSharedPointer)
 
     template <class X, IfCompatible<X> = true>
     QSharedPointer(QSharedPointer<X> &&other) noexcept
@@ -563,8 +558,7 @@ public:
         other.d = nullptr;
         other.value = nullptr;
     }
-    QWeakPointer &operator=(QWeakPointer &&other) noexcept
-    { QWeakPointer moved(std::move(other)); swap(moved); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_MOVE_AND_SWAP(QWeakPointer)
     QWeakPointer &operator=(const QWeakPointer &other) noexcept
     {
         QWeakPointer copy(other);

src/corelib/tools/qversionnumber.h

@@ -126,10 +126,11 @@ class QVersionNumber
             other.dummy = 1;
         }
 
-        SegmentStorage &operator=(SegmentStorage &&other) noexcept
+        QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(SegmentStorage)
+
+        void swap(SegmentStorage &other) noexcept
         {
             qSwap(dummy, other.dummy);
-            return *this;
         }
 
         explicit SegmentStorage(QList<int> &&seg)

src/gui/image/qicon.h

@@ -62,14 +62,13 @@ public:
     QIcon(const QPixmap &pixmap);
     QIcon(const QIcon &other);
     QIcon(QIcon &&other) noexcept
-        : d(other.d)
-    { other.d = nullptr; }
+        : d(qExchange(other.d, nullptr))
+    {}
     explicit QIcon(const QString &fileName); // file or resource name
     explicit QIcon(QIconEngine *engine);
     ~QIcon();
     QIcon &operator=(const QIcon &other);
-    inline QIcon &operator=(QIcon &&other) noexcept
-    { swap(other); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_MOVE_AND_SWAP(QIcon)
     inline void swap(QIcon &other) noexcept
     { qSwap(d, other.d); }
     bool operator==(const QIcon &) const = delete;

src/gui/image/qimage.h

@@ -125,13 +125,12 @@ public:
 
     QImage(const QImage &);
     inline QImage(QImage &&other) noexcept
-        : QPaintDevice(), d(nullptr)
-    { qSwap(d, other.d); }
+        : QPaintDevice(), d(qExchange(other.d, nullptr))
+    {}
     ~QImage();
 
     QImage &operator=(const QImage &);
-    inline QImage &operator=(QImage &&other) noexcept
-    { qSwap(d, other.d); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_MOVE_AND_SWAP(QImage)
     inline void swap(QImage &other) noexcept
     { qSwap(d, other.d); }
 

src/gui/image/qpicture.h

@@ -77,8 +77,7 @@ public:
     void setBoundingRect(const QRect &r);
 
     QPicture& operator=(const QPicture &p);
-    inline QPicture &operator=(QPicture &&other) noexcept
-    { qSwap(d_ptr, other.d_ptr); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QPicture)
     inline void swap(QPicture &other) noexcept
     { d_ptr.swap(other.d_ptr); }
     void detach();

src/gui/image/qpixmap.h

@@ -75,8 +75,7 @@ public:
     ~QPixmap();
 
     QPixmap &operator=(const QPixmap &);
-    inline QPixmap &operator=(QPixmap &&other) noexcept
-    { qSwap(data, other.data); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_MOVE_AND_SWAP(QPixmap)
     inline void swap(QPixmap &other) noexcept
     { qSwap(data, other.data); }
     bool operator==(const QPixmap &) const = delete;

src/gui/kernel/qcursor.h

@@ -87,9 +87,8 @@ public:
     QCursor(const QCursor &cursor);
     ~QCursor();
     QCursor &operator=(const QCursor &cursor);
-    QCursor(QCursor &&other) noexcept : d(other.d) { other.d = nullptr; }
-    inline QCursor &operator=(QCursor &&other) noexcept
-    { swap(other); return *this; }
+    QCursor(QCursor &&other) noexcept : d(qExchange(other.d, nullptr)) {}
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_MOVE_AND_SWAP(QCursor)
 
     void swap(QCursor &other) noexcept { qSwap(d, other.d); }
 

src/gui/kernel/qkeysequence.h

@@ -185,7 +185,7 @@ public:
     operator QVariant() const;
     QKeyCombination operator[](uint i) const;
     QKeySequence &operator=(const QKeySequence &other);
-    QKeySequence &operator=(QKeySequence &&other) noexcept { swap(other); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QKeySequence)
     void swap(QKeySequence &other) noexcept { qSwap(d, other.d); }
 
     bool operator==(const QKeySequence &other) const;

src/gui/kernel/qpalette.h

@@ -68,12 +68,9 @@ public:
     ~QPalette();
     QPalette &operator=(const QPalette &palette);
     QPalette(QPalette &&other) noexcept
-        : d(other.d), data(other.data)
-    { other.d = nullptr; }
-    inline QPalette &operator=(QPalette &&other) noexcept
-    {
-        swap(other); return *this;
-    }
+        : d(qExchange(other.d, nullptr)), data(other.data)
+    {}
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QPalette)
 
     void swap(QPalette &other) noexcept
     {

src/gui/painting/qbrush.h

@@ -78,8 +78,7 @@ public:
 
     ~QBrush();
     QBrush &operator=(const QBrush &brush);
-    inline QBrush &operator=(QBrush &&other) noexcept
-    { qSwap(d, other.d); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QBrush)
     inline void swap(QBrush &other) noexcept
     { qSwap(d, other.d); }
 

src/gui/painting/qcolorspace.h

@@ -95,12 +95,7 @@ public:
     QColorSpace(QColorSpace &&colorSpace) noexcept
             : d_ptr(qExchange(colorSpace.d_ptr, nullptr))
     { }
-    QColorSpace &operator=(QColorSpace &&colorSpace) noexcept
-    {
-        // Make the deallocation of this->d_ptr happen in ~QColorSpace()
-        QColorSpace(std::move(colorSpace)).swap(*this);
-        return *this;
-    }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_MOVE_AND_SWAP(QColorSpace)
 
     void swap(QColorSpace &colorSpace) noexcept
     { qSwap(d_ptr, colorSpace.d_ptr); }

src/gui/painting/qcolortransform.h

@@ -64,11 +64,7 @@ public:
         QColorTransform{other}.swap(*this);
         return *this;
     }
-    QColorTransform &operator=(QColorTransform &&other) noexcept
-    {
-        QColorTransform{std::move(other)}.swap(*this);
-        return *this;
-    }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_MOVE_AND_SWAP(QColorTransform)
 
     void swap(QColorTransform &other) noexcept { qSwap(d, other.d); }
 

src/gui/painting/qpagelayout.h

@@ -81,7 +81,7 @@ public:
                 const QMarginsF &margins, Unit units = Point,
                 const QMarginsF &minMargins = QMarginsF(0, 0, 0, 0));
     QPageLayout(const QPageLayout &other);
-    QPageLayout &operator=(QPageLayout &&other) noexcept { swap(other); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QPageLayout)
     QPageLayout &operator=(const QPageLayout &other);
     ~QPageLayout();
 

src/gui/painting/qpagesize.h

@@ -232,7 +232,7 @@ public:
                        const QString &name = QString(),
                        SizeMatchPolicy matchPolicy = FuzzyMatch);
     QPageSize(const QPageSize &other);
-    QPageSize &operator=(QPageSize &&other) noexcept { swap(other); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QPageSize)
     QPageSize &operator=(const QPageSize &other);
     ~QPageSize();
 

src/gui/painting/qpainterpath.h

@@ -92,8 +92,7 @@ public:
     explicit QPainterPath(const QPointF &startPoint);
     QPainterPath(const QPainterPath &other);
     QPainterPath &operator=(const QPainterPath &other);
-    inline QPainterPath &operator=(QPainterPath &&other) noexcept
-    { qSwap(d_ptr, other.d_ptr); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QPainterPath)
     ~QPainterPath();
 
     inline void swap(QPainterPath &other) noexcept { d_ptr.swap(other.d_ptr); }

src/gui/painting/qpen.h

@@ -71,9 +71,8 @@ public:
 
     QPen &operator=(const QPen &pen) noexcept;
     QPen(QPen &&other) noexcept
-        : d(other.d) { other.d = nullptr; }
-    QPen &operator=(QPen &&other) noexcept
-    { qSwap(d, other.d); return *this; }
+        : d(qExchange(other.d, nullptr)) {}
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QPen)
     void swap(QPen &other) noexcept { qSwap(d, other.d); }
 
     Qt::PenStyle style() const;

src/gui/painting/qregion.h

@@ -70,12 +70,11 @@ public:
     QRegion(const QPolygon &pa, Qt::FillRule fillRule = Qt::OddEvenFill);
     QRegion(const QRegion &region);
     QRegion(QRegion &&other) noexcept
-        : d(other.d) { other.d = const_cast<QRegionData*>(&shared_empty); }
+        : d(qExchange(other.d, const_cast<QRegionData*>(&shared_empty))) {}
     QRegion(const QBitmap &bitmap);
     ~QRegion();
     QRegion &operator=(const QRegion &);
-    inline QRegion &operator=(QRegion &&other) noexcept
-    { qSwap(d, other.d); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QRegion);
     inline void swap(QRegion &other) noexcept { qSwap(d, other.d); }
     bool isEmpty() const;
     bool isNull() const;

src/gui/text/qfont.h

@@ -252,8 +252,7 @@ public:
     bool operator<(const QFont &) const;
     operator QVariant() const;
     bool isCopyOf(const QFont &) const;
-    inline QFont &operator=(QFont &&other) noexcept
-    { qSwap(d, other.d); qSwap(resolve_mask, other.resolve_mask);  return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QFont)
 
     QString key() const;
 

src/gui/text/qfontengine_p.h

@@ -304,14 +304,11 @@ public:
         explicit Holder(void *p, qt_destroy_func_t d) : ptr(p), destroy_func(d) {}
         ~Holder() { if (ptr && destroy_func) destroy_func(ptr); }
         Holder(Holder &&other) noexcept
-            : ptr(other.ptr),
-              destroy_func(other.destroy_func)
+            : ptr(qExchange(other.ptr, nullptr)),
+              destroy_func(qExchange(other.destroy_func, nullptr))
         {
-            other.ptr = nullptr;
-            other.destroy_func = nullptr;
         }
-        Holder &operator=(Holder &&other) noexcept
-        { swap(other); return *this; }
+        QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(Holder)
 
         void swap(Holder &other) noexcept
         {

src/gui/text/qfontmetrics.h

@@ -60,8 +60,7 @@ public:
     ~QFontMetrics();
 
     QFontMetrics &operator=(const QFontMetrics &);
-    inline QFontMetrics &operator=(QFontMetrics &&other) noexcept
-    { qSwap(d, other.d); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QFontMetrics)
 
     void swap(QFontMetrics &other) noexcept
     { qSwap(d, other.d); }
@@ -131,8 +130,7 @@ public:
 
     QFontMetricsF &operator=(const QFontMetricsF &);
     QFontMetricsF &operator=(const QFontMetrics &);
-    inline QFontMetricsF &operator=(QFontMetricsF &&other) noexcept
-    { qSwap(d, other.d); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QFontMetricsF)
 
     void swap(QFontMetricsF &other) noexcept { qSwap(d, other.d); }
 

src/gui/text/qglyphrun.h

@@ -66,7 +66,7 @@ public:
 
     QGlyphRun();
     QGlyphRun(const QGlyphRun &other);
-    QGlyphRun &operator=(QGlyphRun &&other) noexcept { swap(other); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QGlyphRun)
     QGlyphRun &operator=(const QGlyphRun &other);
     ~QGlyphRun();
 

src/gui/text/qrawfont.h

@@ -79,7 +79,7 @@ public:
              qreal pixelSize,
              QFont::HintingPreference hintingPreference = QFont::PreferDefaultHinting);
     QRawFont(const QRawFont &other);
-    QRawFont &operator=(QRawFont &&other) noexcept { swap(other); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QRawFont)
     QRawFont &operator=(const QRawFont &other);
     ~QRawFont();
 

src/gui/text/qstatictext.h

@@ -64,7 +64,7 @@ public:
     QStaticText();
     explicit QStaticText(const QString &text);
     QStaticText(const QStaticText &other);
-    QStaticText &operator=(QStaticText &&other) noexcept { swap(other); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QStaticText)
     QStaticText &operator=(const QStaticText &);
     ~QStaticText();
 

src/gui/text/qtextcursor.h

@@ -73,7 +73,7 @@ public:
     explicit QTextCursor(QTextFrame *frame);
     explicit QTextCursor(const QTextBlock &block);
     QTextCursor(const QTextCursor &cursor);
-    QTextCursor &operator=(QTextCursor &&other) noexcept { swap(other); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QTextCursor)
     QTextCursor &operator=(const QTextCursor &other);
     ~QTextCursor();
 

src/opengl/qopengldebug.h

@@ -109,7 +109,7 @@ public:
     QOpenGLDebugMessage(const QOpenGLDebugMessage &debugMessage);
 
     QOpenGLDebugMessage &operator=(const QOpenGLDebugMessage &debugMessage);
-    QOpenGLDebugMessage &operator=(QOpenGLDebugMessage &&other) noexcept { swap(other); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QOpenGLDebugMessage)
     ~QOpenGLDebugMessage();
 
     void swap(QOpenGLDebugMessage &other) noexcept { qSwap(d, other.d); }

src/opengl/qopenglpixeltransferoptions.h

@@ -55,8 +55,7 @@ class Q_OPENGL_EXPORT QOpenGLPixelTransferOptions
 public:
     QOpenGLPixelTransferOptions();
     QOpenGLPixelTransferOptions(const QOpenGLPixelTransferOptions &);
-    QOpenGLPixelTransferOptions &operator=(QOpenGLPixelTransferOptions &&other) noexcept
-    { swap(other); return *this; }
+    QT_MOVE_ASSIGNMENT_OPERATOR_IMPL_VIA_PURE_SWAP(QOpenGLPixelTransferOptions)
     QOpenGLPixelTransferOptions &operator=(const QOpenGLPixelTransferOptions &);
     ~QOpenGLPixelTransferOptions();