QPointerUniqueId: make fit for release

- Declare as Q_MOVABLE_TYPE
- Prevent QList<QPointerUniqueId> from being instantiated
  (use QVector instead)
- Add equality relational operators
- Add qHash() overload
- Replace non-default ctor with named ctor.
- Add Q_DECL_NOTHROW.
- Add Q_DECL_CONSTEXPR.
- Rename numeric() -> numericId().
- Update docs.

The extension vector for this class calls for additional
properties to be added later, but these are not user-
settable. It thus suffices to rely on the only data
member, a qint64, which can be reinterpreted to an index
into an array or hash with actual objects. This allows
to make the class a Trivial Type (ie. no overhead over
an int) while still supporting later extension. Cf.
QSslEllipticCurve as another example of such a class.

The extension has to maintain the following invariants,
encoded into user code by way of being used in inline
functions:

- m_numericId == -1 <=> !isValid()

This is trivial to support. An extension could not and
still cannot reinterpret the qint64 member as a d-pointer,
but a d-pointer is only necessary for user-settable
properties where updating a central private data structure
would cause too much contention.

Add a test.

Since this type is used in other modules, keep the existing
functions, but mark them as deprecated with the expectation
that these compat functions be removed before 5.8.0 final.

Task-number: QTBUG-54616
Change-Id: Ia3ede0ecaeeef4cd3ffa94a72b1050bd409713a5
Reviewed-by: Shawn Rutledge <shawn.rutledge@qt.io>

1 files changed, 73 insertions, 9 deletions

diff --git a/src/gui/kernel/qevent.cpp b/src/gui/kernel/qevent.cpp
index 254b8926c8..72cd374419 100644
--- a/src/gui/kernel/qevent.cpp
+++ b/src/gui/kernel/qevent.cpp
@@ -44,6 +44,7 @@
 #include "qpa/qplatformdrag.h"
 #include "private/qevent_p.h"
 #include "qfile.h"
+#include "qhashfunctions.h"
 #include "qmetaobject.h"
 #include "qmimedata.h"
 #include "private/qdnd_p.h"
@@ -4474,7 +4475,7 @@ int QTouchEvent::TouchPoint::id() const
     \since 5.8
     Returns the unique ID of this touch point or token, if any.
 
-    It is normally invalid (with a \l {QPointerUniqueId::numeric()} {numeric()} value of -1),
+    It is normally invalid (see \l {QPointerUniqueId::isValid()} {isValid()}),
     because touchscreens cannot uniquely identify fingers. But when the
     \l {TouchPoint::InfoFlag} {Token} flag is set, it is expected to uniquely
     identify a specific token (fiducial object).
@@ -4757,7 +4758,7 @@ void QTouchEvent::TouchPoint::setUniqueId(qint64 uid)
 {
     if (d->ref.load() != 1)
         d = d->detach();
-    d->uniqueId = QPointerUniqueId(uid);
+    d->uniqueId = QPointerUniqueId::fromNumericId(uid);
 }
 
 /*! \internal */
@@ -5184,28 +5185,91 @@ Qt::ApplicationState QApplicationStateChangeEvent::applicationState() const
     \brief QPointerUniqueId identifies a unique object, such as a tagged token
     or stylus, which is used with a pointing device.
 
+    QPointerUniqueIds can be compared for equality, and can be used as keys in a QHash.
+    You get access to the numerical ID via numericId(), if the device supports such IDs.
+    For future extensions, though, you should not use that function, but compare objects
+    of this type using the equality operator.
+
+    This class is a thin wrapper around an integer ID. You pass it into and out of
+    functions by value.
+
+    This type actively prevents you from holding it in a QList, because doing so would
+    be very inefficient. Use a QVector instead, which has the same API as QList, but more
+    efficient storage.
+
     \sa QTouchEvent::TouchPoint
 */
 
 /*!
-    Constructs a unique pointer ID with a numeric \a id provided by the hardware.
-    The default is -1, which means an invalid pointer ID.
+    \fn QPointerUniqueId::QPointerUniqueId()
+    Constructs an invalid unique pointer ID.
+*/
+
+/*!
+    Constructs a unique pointer ID from numeric ID \a id.
 */
-QPointerUniqueId::QPointerUniqueId(qint64 id)
-    : m_numericId(id)
+QPointerUniqueId QPointerUniqueId::fromNumericId(qint64 id)
 {
+    QPointerUniqueId result;
+    result.m_numericId = id;
+    return result;
 }
 
 /*!
-    \property QPointerUniqueId::numeric
+    \fn bool QPointerUniqueId::isValid()
+
+    Returns whether this unique pointer ID is valid, that is, it represents an actual
+    pointer.
+*/
+
+/*!
+    \property QPointerUniqueId::numericId
     \brief the numeric unique ID of the token represented by a touchpoint
 
-    This is the numeric unique ID if the device provides that type of ID;
+    If the device provides a numeric ID, isValid() returns true, and this
+    property provides the numeric ID;
     otherwise it is -1.
+
+    You should not use the value of this property in portable code, but
+    instead rely on equality to identify pointers.
+
+    \sa isValid()
 */
-qint64 QPointerUniqueId::numeric() const
+qint64 QPointerUniqueId::numericId() const Q_DECL_NOTHROW
 {
     return m_numericId;
 }
 
+/*!
+    \relates QPointerUniqueId
+    \since 5.8
+
+    Returns whether the two unique pointer IDs \a lhs and \a rhs identify the same pointer
+    (\c true) or not (\c false).
+*/
+bool operator==(QPointerUniqueId lhs, QPointerUniqueId rhs) Q_DECL_NOTHROW
+{
+    return lhs.numericId() == rhs.numericId();
+}
+
+/*!
+    \fn bool operator!=(QPointerUniqueId lhs, QPointerUniqueId rhs)
+    \relates QPointerUniqueId
+    \since 5.8
+
+    Returns whether the two unique pointer IDs \a lhs and \a rhs identify different pointers
+    (\c true) or not (\c false).
+*/
+
+/*!
+    \relates QPointerUniqueId
+    \since 5.8
+
+    Returns the hash value for \a key, using \a seed to seed the calculation.
+*/
+uint qHash(QPointerUniqueId key, uint seed) Q_DECL_NOTHROW
+{
+    return qHash(key.numericId(), seed);
+}
+
 QT_END_NAMESPACE