Deprecate QVariant::operator< and related operators

Since the operator does not have a total order, it is kind of pointless,
and this is going to be removed in Qt6

Change-Id: I754be059726bf30993550a2d753f8b865f2d4a5f
Reviewed-by: Lars Knoll <lars.knoll@qt.io>
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>

2 files changed, 20 insertions, 4 deletions

diff --git a/src/corelib/kernel/qvariant.cpp b/src/corelib/kernel/qvariant.cpp
index 762a761026..d1eb463514 100644
--- a/src/corelib/kernel/qvariant.cpp
+++ b/src/corelib/kernel/qvariant.cpp
@@ -3829,6 +3829,7 @@ bool QVariant::convert(const int type, void *ptr) const
 
 /*!
     \fn bool QVariant::operator<(const QVariant &v) const
+    \obsolete
 
     Compares this QVariant with \a v and returns \c true if this is less than \a v.
 
@@ -3838,10 +3839,15 @@ bool QVariant::convert(const int type, void *ptr) const
     \warning To make this function work with a custom type registered with
     qRegisterMetaType(), its comparison operator must be registered using
     QMetaType::registerComparators().
+
+    This operator is deprecated as it cannot establish a total order required
+    for most use of this operator, which is the reason you cannot use QVariant
+    as the key of a QMap.
 */
 
 /*!
     \fn bool QVariant::operator<=(const QVariant &v) const
+    \obsolete
 
     Compares this QVariant with \a v and returns \c true if this is less or equal than \a v.
 
@@ -3851,10 +3857,13 @@ bool QVariant::convert(const int type, void *ptr) const
     \warning To make this function work with a custom type registered with
     qRegisterMetaType(), its comparison operator must be registered using
     QMetaType::registerComparators().
+
+    This operator is deprecated as it cannot establish a total order.
 */
 
 /*!
     \fn bool QVariant::operator>(const QVariant &v) const
+    \obsolete
 
     Compares this QVariant with \a v and returns \c true if this is larger than \a v.
 
@@ -3864,10 +3873,13 @@ bool QVariant::convert(const int type, void *ptr) const
     \warning To make this function work with a custom type registered with
     qRegisterMetaType(), its comparison operator must be registered using
     QMetaType::registerComparators().
+
+    This operator is deprecated as it cannot establish a total order.
 */
 
 /*!
     \fn bool QVariant::operator>=(const QVariant &v) const
+    \obsolete
 
     Compares this QVariant with \a v and returns \c true if this is larger or equal than \a v.
 
@@ -3877,6 +3889,8 @@ bool QVariant::convert(const int type, void *ptr) const
     \warning To make this function work with a custom type registered with
     qRegisterMetaType(), its comparison operator must be registered using
     QMetaType::registerComparators().
+
+    This operator is deprecated as it cannot establish a total order.
 */
 
 static bool qIsNumericType(uint tp)
diff --git a/src/corelib/kernel/qvariant.h b/src/corelib/kernel/qvariant.h
index 86c7414704..6e27c9bf1f 100644
--- a/src/corelib/kernel/qvariant.h
+++ b/src/corelib/kernel/qvariant.h
@@ -463,14 +463,16 @@ class Q_CORE_EXPORT QVariant
     { return cmp(v); }
     inline bool operator!=(const QVariant &v) const
     { return !cmp(v); }
-    inline bool operator<(const QVariant &v) const
+#if QT_DEPRECATED_SINCE(5, 15)
+    QT_DEPRECATED inline bool operator<(const QVariant &v) const
     { return compare(v) < 0; }
-    inline bool operator<=(const QVariant &v) const
+    QT_DEPRECATED inline bool operator<=(const QVariant &v) const
     { return compare(v) <= 0; }
-    inline bool operator>(const QVariant &v) const
+    QT_DEPRECATED inline bool operator>(const QVariant &v) const
     { return compare(v) > 0; }
-    inline bool operator>=(const QVariant &v) const
+    QT_DEPRECATED inline bool operator>=(const QVariant &v) const
     { return compare(v) >= 0; }
+#endif
 
 protected:
     friend inline bool operator==(const QVariant &, const QVariantComparisonHelper &);