QList: Introduce constFirst() and constEnd()

Allows to easily prevent detaching in common code like: getList().first()

[ChangeLog][QtCore][QList] Added the convenience constFirst and constLast functions.

Task-number: QTBUG-46026
Change-Id: I51ecb51fe91fc7d993ad35b5c7392f4da88e5f7b
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

2 files changed, 24 insertions, 2 deletions

diff --git a/src/corelib/tools/qlist.cpp b/src/corelib/tools/qlist.cpp
index f4901d336e..d774548d3a 100644
--- a/src/corelib/tools/qlist.cpp
+++ b/src/corelib/tools/qlist.cpp
@@ -1227,7 +1227,7 @@ void **QListData::erase(void **xi)
     not be empty. If the list can be empty, call isEmpty() before
     calling this function.
 
-    \sa last(), isEmpty()
+    \sa constFirst(), last(), isEmpty()
 */
 
 /*! \fn const T& QList::first() const
@@ -1235,13 +1235,23 @@ void **QListData::erase(void **xi)
     \overload
 */
 
+/*! \fn const T& QList::constFirst() const
+    \since 5.6
+
+    Returns a const reference to the first item in the list. The list must
+    not be empty. If the list can be empty, call isEmpty() before
+    calling this function.
+
+    \sa constLast(), isEmpty(), first()
+*/
+
 /*! \fn T& QList::last()
 
     Returns a reference to the last item in the list.  The list must
     not be empty. If the list can be empty, call isEmpty() before
     calling this function.
 
-    \sa first(), isEmpty()
+    \sa constLast(), first(), isEmpty()
 */
 
 /*! \fn const T& QList::last() const
@@ -1249,6 +1259,16 @@ void **QListData::erase(void **xi)
     \overload
 */
 
+/*! \fn const T& QList::constLast() const
+    \since 5.6
+
+    Returns a reference to the last item in the list. The list must
+    not be empty. If the list can be empty, call isEmpty() before
+    calling this function.
+
+    \sa constFirst(), isEmpty(), last()
+*/
+
 /*! \fn void QList::removeFirst()
 
     Removes the first item in the list. Calling this function is
diff --git a/src/corelib/tools/qlist.h b/src/corelib/tools/qlist.h
index e446a6625b..ac46dc3244 100644
--- a/src/corelib/tools/qlist.h
+++ b/src/corelib/tools/qlist.h
@@ -331,9 +331,11 @@ public:
     inline int count() const { return p.size(); }
     inline int length() const { return p.size(); } // Same as count()
     inline T& first() { Q_ASSERT(!isEmpty()); return *begin(); }
+    inline const T& constFirst() const { return first(); }
     inline const T& first() const { Q_ASSERT(!isEmpty()); return at(0); }
     T& last() { Q_ASSERT(!isEmpty()); return *(--end()); }
     const T& last() const { Q_ASSERT(!isEmpty()); return at(count() - 1); }
+    inline const T& constLast() const { return last(); }
     inline void removeFirst() { Q_ASSERT(!isEmpty()); erase(begin()); }
     inline void removeLast() { Q_ASSERT(!isEmpty()); erase(--end()); }
     inline bool startsWith(const T &t) const { return !isEmpty() && first() == t; }