QPen: add move constructor

After this change, the relation between copy/move constructor calls in QtGui is
something like 40/16.

A moved-from QPen can only be copied, assigned-to or else destroyed. This required
adding a nullptr check to the copy ctor and the dtor and rewriting copy assignment
(which used non-nullptr-safe qAtomicAssign) in terms of copy construction and
swapping.

Extensive tests included. They are implemented such that they work in C++98 as well
as C++11 mode, but they naturally test move semantics only in a C++11 build.

Change-Id: If68f37c10b8eeefb2478cbae386cd2e38b4f6e19
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 15 insertions, 3 deletions

diff --git a/src/gui/painting/qpen.cpp b/src/gui/painting/qpen.cpp
index c0b3769c2d..b661057f64 100644
--- a/src/gui/painting/qpen.cpp
+++ b/src/gui/painting/qpen.cpp
@@ -327,17 +327,29 @@ QPen::QPen(const QBrush &brush, qreal width, Qt::PenStyle s, Qt::PenCapStyle c,
 QPen::QPen(const QPen &p)
 {
     d = p.d;
-    d->ref.ref();
+    if (d)
+        d->ref.ref();
 }
 
 
 /*!
+    \fn QPen::QPen(QPen &&pen)
+    \since 5.4
+
+    Constructs a pen that is moved from the given \a pen.
+
+    The moved-from pen can only be assigned to, copied, or
+    destroyed. Any other operation (prior to assignment) leads to
+    undefined behavior.
+*/
+
+/*!
     Destroys the pen.
 */
 
 QPen::~QPen()
 {
-    if (!d->ref.deref())
+    if (d && !d->ref.deref())
         delete d;
 }
 
@@ -373,7 +385,7 @@ void QPen::detach()
 
 QPen &QPen::operator=(const QPen &p)
 {
-    qAtomicAssign(d, p.d);
+    QPen(p).swap(*this);
     return *this;
 }