QSizePolicy: add a transposed() method

In some situations, this allows for nicer code. It's also possible to
make this constexpr in C++11, whereas the mutable transpose() would
require C++14-style constexpr.

The new function should also be faster, since it just swaps the member
variables.

Because of constexpr-function limitations, the way the return value is
constructed needs to depend on the level of the compiler's C++11 support.
This is not the only class that requires uniform init to provide a fully
constexpr interface (QUuid and QBasicAtomic come to mind), so this should
probably be generalized across Qt at some point.

Added tests.

[ChangeLog][QtWidgets][QSizePolicy] Added transposed() method.

Change-Id: Ic1077a0d5a861e7c63bd1daeeb42b97c3a2f71ef
Reviewed-by: Sérgio Martins <sergio.martins@kdab.com>

src/widgets/kernel/qsizepolicy.cpp

@@ -395,6 +395,18 @@ void QSizePolicy::setControlType(ControlType type)
     \fn void QSizePolicy::transpose()
 
     Swaps the horizontal and vertical policies and stretches.
+
+    \sa transposed()
+*/
+
+/*!
+    \fn QSizePolicy QSizePolicy::transposed()
+    \since 5.9
+
+    Returns a size policy object with the horizontal and vertical
+    policies and stretches swapped.
+
+    \sa transpose()
 */
 
 /*!

src/widgets/kernel/qsizepolicy.h

@@ -49,11 +49,25 @@ QT_BEGIN_NAMESPACE
 // https://gcc.gnu.org/bugzilla/show_bug.cgi?id=54922
 #if !defined(Q_CC_GNU) || defined(Q_CC_INTEL) || defined(Q_CC_CLANG) || Q_CC_GNU >= 408
 # define QT_SIZEPOLICY_CONSTEXPR Q_DECL_CONSTEXPR
+# if defined(Q_COMPILER_UNIFORM_INIT)
+#  define QT_SIZEPOLICY_CONSTEXPR_AND_UNIFORM_INIT Q_DECL_CONSTEXPR
+#  if defined(Q_COMPILER_CONSTEXPR)
+#   define QT_SIZEPOLICY_RETURN_BITS(E1, E2, E3, E4, E5, E6, E7, E8) \
+        return Bits{ E1, E2, E3, E4, E5, E6, E7, E8 }
+#  endif // constexpr && uniform-init
+# endif // uniform-init
 #endif
 
 #ifndef QT_SIZEPOLICY_CONSTEXPR
 # define QT_SIZEPOLICY_CONSTEXPR
 #endif
+#ifndef QT_SIZEPOLICY_CONSTEXPR_AND_UNIFORM_INIT
+# define QT_SIZEPOLICY_CONSTEXPR_AND_UNIFORM_INIT
+#endif
+#ifndef QT_SIZEPOLICY_RETURN_BITS
+# define QT_SIZEPOLICY_RETURN_BITS(E1, E2, E3, E4, E5, E6, E7, E8) \
+    const Bits result = { E1, E2, E3, E4, E5, E6, E7, E8 }; return result
+#endif
 
 class QVariant;
 class QSizePolicy;
@@ -145,6 +159,13 @@ public:
     void setRetainSizeWhenHidden(bool retainSize) { bits.retainSizeWhenHidden = retainSize; }
 
     void transpose();
+#ifndef Q_QDOC
+    QT_SIZEPOLICY_CONSTEXPR_AND_UNIFORM_INIT
+#endif
+    QSizePolicy transposed() const Q_DECL_NOTHROW Q_REQUIRED_RESULT
+    {
+        return QSizePolicy(bits.transposed());
+    }
 
 private:
 #ifndef QT_NO_DATASTREAM
@@ -152,6 +173,8 @@ private:
     friend Q_WIDGETS_EXPORT QDataStream &operator>>(QDataStream &, QSizePolicy &);
 #endif
     QT_SIZEPOLICY_CONSTEXPR QSizePolicy(int i) : data(i) { }
+    struct Bits;
+    QT_SIZEPOLICY_CONSTEXPR explicit QSizePolicy(Bits b) Q_DECL_NOTHROW : bits(b) { }
 
     struct Bits {
         quint32 horStretch : 8;
@@ -162,6 +185,19 @@ private:
         quint32 hfw : 1;
         quint32 wfh : 1;
         quint32 retainSizeWhenHidden : 1;
+
+        QT_SIZEPOLICY_CONSTEXPR_AND_UNIFORM_INIT
+        Bits transposed() const Q_DECL_NOTHROW
+        {
+            QT_SIZEPOLICY_RETURN_BITS(verStretch, // \ swap
+                                      horStretch, // /
+                                      verPolicy, // \ swap
+                                      horPolicy, // /
+                                      ctype,
+                                      hfw, // \ don't swap (historic behavior)
+                                      wfh, // /
+                                      retainSizeWhenHidden);
+        }
     };
     union {
         Bits bits;
@@ -196,6 +232,8 @@ inline void QSizePolicy::transpose() {
 }
 
 #undef QT_SIZEPOLICY_CONSTEXPR
+#undef QT_SIZEPOLICY_CONSTEXPR_AND_UNIFORM_INIT
+#undef QT_SIZEPOLICY_RETURN_BITS
 
 QT_END_NAMESPACE
 

tests/auto/widgets/kernel/qsizepolicy/tst_qsizepolicy.cpp

@@ -45,6 +45,8 @@ private Q_SLOTS:
     void defaultValues();
     void getSetCheck_data() { data(); }
     void getSetCheck();
+    void transposed_data() { data(); }
+    void transposed();
     void dataStream();
     void horizontalStretch();
     void verticalStretch();
@@ -161,6 +163,26 @@ void tst_QSizePolicy::getSetCheck()
     QCOMPARE(sp.expandingDirections(), ed);
 }
 
+void tst_QSizePolicy::transposed()
+{
+    FETCH_TEST_DATA;
+
+    const QSizePolicy tr = sp.transposed();
+
+    QCOMPARE(tr.horizontalPolicy(),    vp);  // swapped
+    QCOMPARE(tr.verticalPolicy(),      hp);  // swapped
+    QCOMPARE(tr.horizontalStretch(),   vst); // swapped
+    QCOMPARE(tr.verticalStretch(),     hst); // swapped
+    QCOMPARE(tr.controlType(),         ct);  // not swapped
+    QCOMPARE(tr.hasHeightForWidth(),   hfw); // not swapped (historic behavior)
+    QCOMPARE(tr.hasWidthForHeight(),   wfh); // not swapped (historic behavior)
+    QCOMPARE(tr.expandingDirections(), ed);  // swapped
+
+    // destructive test - keep last:
+    sp.transpose();
+    QCOMPARE(sp, tr);
+}
+
 static void makeRow(QSizePolicy sp, QSizePolicy::Policy hp, QSizePolicy::Policy vp,
                     int hst, int vst, QSizePolicy::ControlType ct, bool hfw, bool wfh,
                     Qt::Orientations orients)