QTaggedPointer: some API cleanups

- don't refer to the class with template arguments in the body of the class
  (incl. one where we got the template args wrong)
- make namespace-level swap a non-member friend
- make default ctor constexpr and non-explicit
  (default ctors should never be explicit)
- make ctor from std::nullptr_t constexpr
- remove op= from std::nullptr (will be handled by op=(T*) anyway)
- pass QTaggedPointer by value (it's a Trivial Type, so can be passed in registers)
- fix missing QTypeInfo for non-default Tag types
- remove unused include limits.h
- make qHash-able (why is the tag ignored?)

Change-Id: Idee1d685ac365c988698a8637fd5df3accfc1396
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

2 files changed, 49 insertions, 31 deletions

diff --git a/src/corelib/tools/qtaggedpointer.h b/src/corelib/tools/qtaggedpointer.h
index 0c48fa6e4f..67209ffc08 100644
--- a/src/corelib/tools/qtaggedpointer.h
+++ b/src/corelib/tools/qtaggedpointer.h
@@ -43,8 +43,7 @@
 #include <QtCore/qglobal.h>
 #include <QtCore/qalgorithms.h>
 #include <QtCore/qmath.h>
-
-#include <limits.h>
+#include <QtCore/qtypeinfo.h>
 
 QT_BEGIN_NAMESPACE
 
@@ -80,10 +79,13 @@ public:
     static constexpr quintptr tagMask() { return QtPrivate::TagInfo<T>::alignment - 1; }
     static constexpr quintptr pointerMask() { return ~tagMask(); }
 
-    explicit QTaggedPointer(T *pointer = nullptr, Tag tag = Tag()) noexcept
+    constexpr QTaggedPointer() noexcept : d(0) {}
+    constexpr QTaggedPointer(std::nullptr_t) noexcept : QTaggedPointer() {}
+
+    explicit QTaggedPointer(T *pointer, Tag tag = Tag()) noexcept
         : d(quintptr(pointer))
     {
-        Q_STATIC_ASSERT(sizeof(Type*) == sizeof(QTaggedPointer<Type>));
+        Q_STATIC_ASSERT(sizeof(Type*) == sizeof(QTaggedPointer));
 
         Q_ASSERT_X((quintptr(pointer) & tagMask()) == 0,
             "QTaggedPointer<T, Tag>", "Pointer is not aligned");
@@ -107,18 +109,12 @@ public:
         return !isNull();
     }
 
-    QTaggedPointer<T, Tag> &operator=(T *other) noexcept
+    QTaggedPointer &operator=(T *other) noexcept
     {
         d = reinterpret_cast<quintptr>(other) | (d & tagMask());
         return *this;
     }
 
-    QTaggedPointer<T, Tag> &operator=(std::nullptr_t) noexcept
-    {
-        d &= tagMask();
-        return *this;
-    }
-
     static constexpr Tag maximumTag() noexcept
     {
         return TagType(typename QtPrivate::TagInfo<T>::TagType(tagMask()));
@@ -147,58 +143,62 @@ public:
         return !data();
     }
 
-    void swap(QTaggedPointer<T, Tag> &other) noexcept
+    void swap(QTaggedPointer &other) noexcept
     {
         qSwap(d, other.d);
     }
 
-    friend inline bool operator==(const QTaggedPointer<T, Tag> &lhs, const QTaggedPointer<T, Tag> &rhs) noexcept
+    friend inline bool operator==(QTaggedPointer lhs, QTaggedPointer rhs) noexcept
     {
         return lhs.data() == rhs.data();
     }
 
-    friend inline bool operator!=(const QTaggedPointer<T, Tag> &lhs, const QTaggedPointer<T, Tag> &rhs) noexcept
+    friend inline bool operator!=(QTaggedPointer lhs, QTaggedPointer rhs) noexcept
     {
         return lhs.data() != rhs.data();
     }
 
-    friend inline bool operator==(const QTaggedPointer<T, Tag> &lhs, std::nullptr_t) noexcept
+    friend inline bool operator==(QTaggedPointer lhs, std::nullptr_t) noexcept
     {
         return lhs.isNull();
     }
 
-    friend inline bool operator==(std::nullptr_t, const QTaggedPointer<T, Tag> &rhs) noexcept
+    friend inline bool operator==(std::nullptr_t, QTaggedPointer rhs) noexcept
     {
         return rhs.isNull();
     }
 
-    friend inline bool operator!=(const QTaggedPointer<T, Tag> &lhs, std::nullptr_t) noexcept
+    friend inline bool operator!=(QTaggedPointer lhs, std::nullptr_t) noexcept
     {
         return !lhs.isNull();
     }
 
-    friend inline bool operator!=(std::nullptr_t, const QTaggedPointer<T, Tag> &rhs) noexcept
+    friend inline bool operator!=(std::nullptr_t, QTaggedPointer rhs) noexcept
     {
         return !rhs.isNull();
     }
 
-    friend inline bool operator!(const QTaggedPointer<T, Tag> &ptr) noexcept
+    friend inline bool operator!(QTaggedPointer ptr) noexcept
     {
         return !ptr.data();
     }
 
+    friend inline void swap(QTaggedPointer &p1, QTaggedPointer &p2) noexcept
+    {
+        p1.swap(p2);
+    }
+
 protected:
     quintptr d;
 };
 
-template <typename T>
-Q_DECLARE_TYPEINFO_BODY(QTaggedPointer<T>, Q_MOVABLE_TYPE);
+template <typename T, typename Tag>
+constexpr inline std::size_t qHash(QTaggedPointer<T, Tag> p, std::size_t seed = 0) noexcept
+{ return qHash(p.data(), seed); }
 
 template <typename T, typename Tag>
-inline void swap(QTaggedPointer<T, Tag> &p1, QTaggedPointer<T, Tag> &p2) noexcept
-{
-    p1.swap(p2);
-}
+class QTypeInfo<QTaggedPointer<T, Tag>>
+    : public QTypeInfoMerger<QTaggedPointer<T, Tag>, quintptr> {};
 
 QT_END_NAMESPACE
 
diff --git a/src/corelib/tools/qtaggedpointer.qdoc b/src/corelib/tools/qtaggedpointer.qdoc
index 5b335e8739..303b89232c 100644
--- a/src/corelib/tools/qtaggedpointer.qdoc
+++ b/src/corelib/tools/qtaggedpointer.qdoc
@@ -93,6 +93,18 @@
 
 
 /*!
+    \fn template <typename T, typename Tag> QTaggedPointer<T, Tag>::QTaggedPointer()
+
+    Creates a tagged pointer that contains nullptr and stores no tag.
+*/
+
+/*!
+    \fn template <typename T, typename Tag> QTaggedPointer<T, Tag>::QTaggedPointer(std::nullptr_t)
+
+    Creates a tagged pointer that contains nullptr and stores no tag.
+*/
+
+/*!
     \fn template <typename T, typename Tag> explicit QTaggedPointer<T, Tag>::QTaggedPointer(T *pointer = nullptr, Tag tag = Tag()) noexcept
 
     Creates a tagged pointer that points to \a pointer and stores the specified \a tag.
@@ -159,7 +171,7 @@
 */
 
 /*!
-    \fn template <typename T, typename Tag> inline bool operator==(const QTaggedPointer<T, Tag> &lhs, const QTaggedPointer<T, Tag> &rhs) noexcept
+    \fn template <typename T, typename Tag> inline bool operator==(QTaggedPointer lhs, QTaggedPointer rhs) noexcept
     \relates QTaggedPointer
 
     Returns \c true if \a lhs is equal to \a rhs; otherwise returns \c false.
@@ -168,7 +180,7 @@
 */
 
 /*!
-    \fn template <typename T, typename Tag> inline bool operator!=(const QTaggedPointer<T, Tag> &lhs, const QTaggedPointer<T, Tag> &rhs) noexcept
+    \fn template <typename T, typename Tag> inline bool operator!=(QTaggedPointer lhs, QTaggedPointer rhs) noexcept
     \relates QTaggedPointer
 
     Returns \c true if \a lhs is not equal to \a rhs; otherwise returns \c false.
@@ -177,30 +189,36 @@
 */
 
 /*!
-    \fn template <typename T, typename Tag> inline bool operator==(const QTaggedPointer<T, Tag> &lhs, std::nullptr_t) noexcept
+    \fn template <typename T, typename Tag> inline bool operator==(QTaggedPointer lhs, std::nullptr_t) noexcept
     \relates QTaggedPointer
 
     Returns \c true if \a lhs refers to \c nullptr.
 */
 
 /*!
-    \fn template <typename T, typename Tag> inline bool operator==(std::nullptr_t, const QTaggedPointer<T, Tag> &rhs) noexcept
+    \fn template <typename T, typename Tag> inline bool operator==(std::nullptr_t, QTaggedPointer rhs) noexcept
     \relates QTaggedPointer
 
     Returns \c true if \a rhs refers to \c nullptr.
 */
 
 /*!
-    \fn template <typename T, typename Tag> inline bool operator!=(const QTaggedPointer<T, Tag> &lhs, std::nullptr_t) noexcept
+    \fn template <typename T, typename Tag> inline bool operator!=(QTaggedPointerlhs, std::nullptr_t) noexcept
     \relates QTaggedPointer
 
     Returns \c true if \a lhs refers to a valid (i.e. non-null) pointer.
 */
 
 /*!
-    \fn template <typename T, typename Tag> inline bool operator!=(std::nullptr_t, const QTaggedPointer<T, Tag> &rhs) noexcept
+    \fn template <typename T, typename Tag> inline bool operator!=(std::nullptr_t, QTaggedPointer rhs) noexcept
     \relates QTaggedPointer
 
     Returns \c true if \a rhs refers to a valid (i.e. non-null) pointer.
 */
 
+/*!
+    \fn template <typename T, typename Tag> qHash(QTaggedPointer<T, Tag> key, std::size_t seed)
+    \relates QTaggedPointer
+
+    Returns the hash value for the \a key, using \a seed to seed the calculation.
+*/