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>

5 files changed, 6 insertions, 11 deletions

diff --git a/src/corelib/text/qbytearray.h b/src/corelib/text/qbytearray.h
index 8f5e1d9f7f..60f1bd01f5 100644
--- a/src/corelib/text/qbytearray.h
+++ b/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); }
 
diff --git a/src/corelib/text/qcollator.h b/src/corelib/text/qcollator.h
index de8c8b7e3c..793d1cedd4 100644
--- a/src/corelib/text/qcollator.h
+++ b/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); }
diff --git a/src/corelib/text/qlocale.h b/src/corelib/text/qlocale.h
index 0ff2e4d469..8b49eb89f9 100644
--- a/src/corelib/text/qlocale.h
+++ b/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();
 
diff --git a/src/corelib/text/qregularexpression.h b/src/corelib/text/qregularexpression.h
index ee6c421399..6067d94c76 100644
--- a/src/corelib/text/qregularexpression.h
+++ b/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); }
 
diff --git a/src/corelib/text/qstring.h b/src/corelib/text/qstring.h
index ea78dd017f..0e564b20ed 100644
--- a/src/corelib/text/qstring.h
+++ b/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; }