Containers: destroy previous state on move-assignment immediately

[ChangeLog][QtCore] All generic containers (with the exception of
QVarLengthArray, but including QSharedPointer) destroy the
previous state as part of a move-assignment now. Previously, they
would dump it into the right-hand-side object. Note that this is
only true for the generic containers. Other implicitly-shared
types, as well as the non-generic containers QString, QByteArray,
etc. still just swap the contents with the right-hand-side object
when move-assigned into, and, for performance reasons, this will
not change in the forseeable future.

Change-Id: I1f1c684e85400b77bd2e7fba65bde2dce6c1bdde
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@theqtcompany.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

5 files changed, 6 insertions, 5 deletions

diff --git a/src/corelib/tools/qhash.h b/src/corelib/tools/qhash.h
index c83dcaabe1..5a4175ec5d 100644
--- a/src/corelib/tools/qhash.h
+++ b/src/corelib/tools/qhash.h
@@ -249,7 +249,7 @@ public:
 #ifdef Q_COMPILER_RVALUE_REFS
     QHash(QHash &&other) Q_DECL_NOTHROW : d(other.d) { other.d = const_cast<QHashData *>(&QHashData::shared_null); }
     QHash &operator=(QHash &&other) Q_DECL_NOTHROW
-    { qSwap(d, other.d); return *this; }
+    { QHash moved(std::move(other)); swap(moved); return *this; }
 #endif
     void swap(QHash &other) Q_DECL_NOTHROW { qSwap(d, other.d); }
 
diff --git a/src/corelib/tools/qlinkedlist.h b/src/corelib/tools/qlinkedlist.h
index 7908bf5137..f216aa121c 100644
--- a/src/corelib/tools/qlinkedlist.h
+++ b/src/corelib/tools/qlinkedlist.h
@@ -88,7 +88,7 @@ public:
 #ifdef Q_COMPILER_RVALUE_REFS
     inline QLinkedList(QLinkedList<T> &&other) : d(other.d) { other.d = const_cast<QLinkedListData *>(&QLinkedListData::shared_null); }
     inline QLinkedList<T> &operator=(QLinkedList<T> &&other)
-    { qSwap(d, other.d); return *this; }
+    { QLinkedList moved(std::move(other)); swap(moved); return *this; }
 #endif
     inline void swap(QLinkedList<T> &other) { qSwap(d, other.d); }
     bool operator==(const QLinkedList<T> &l) const;
diff --git a/src/corelib/tools/qlist.h b/src/corelib/tools/qlist.h
index b895e7e7b6..e1804e17e5 100644
--- a/src/corelib/tools/qlist.h
+++ b/src/corelib/tools/qlist.h
@@ -144,7 +144,7 @@ public:
 #ifdef Q_COMPILER_RVALUE_REFS
     inline QList(QList<T> &&other) : d(other.d) { other.d = const_cast<QListData::Data *>(&QListData::shared_null); }
     inline QList &operator=(QList<T> &&other)
-    { qSwap(d, other.d); return *this; }
+    { QList moved(std::move(other)); swap(moved); return *this; }
 #endif
     inline void swap(QList<T> &other) { qSwap(d, other.d); }
 #ifdef Q_COMPILER_INITIALIZER_LISTS
diff --git a/src/corelib/tools/qmap.h b/src/corelib/tools/qmap.h
index bf0a36aa88..f3d921c968 100644
--- a/src/corelib/tools/qmap.h
+++ b/src/corelib/tools/qmap.h
@@ -344,7 +344,7 @@ public:
     }
 
     inline QMap<Key, T> &operator=(QMap<Key, T> &&other)
-    { qSwap(d, other.d); return *this; }
+    { QMap moved(std::move(other)); swap(moved); return *this; }
 #endif
     inline void swap(QMap<Key, T> &other) { qSwap(d, other.d); }
     explicit QMap(const typename std::map<Key, T> &other);
diff --git a/src/corelib/tools/qvector.h b/src/corelib/tools/qvector.h
index 2adb047ed9..624d828a3b 100644
--- a/src/corelib/tools/qvector.h
+++ b/src/corelib/tools/qvector.h
@@ -70,7 +70,8 @@ public:
     QVector<T> &operator=(const QVector<T> &v);
 #ifdef Q_COMPILER_RVALUE_REFS
     QVector(QVector<T> &&other) Q_DECL_NOTHROW : d(other.d) { other.d = Data::sharedNull(); }
-    QVector<T> &operator=(QVector<T> &&other) Q_DECL_NOTHROW { swap(other); return *this; }
+    QVector<T> &operator=(QVector<T> &&other) Q_DECL_NOTHROW
+    { QVector moved(std::move(other)); swap(moved); return *this; }
 #endif
     void swap(QVector<T> &other) Q_DECL_NOTHROW { qSwap(d, other.d); }
 #ifdef Q_COMPILER_INITIALIZER_LISTS