Add support for first(n), last(n) and sliced() to QList

This keeps the API symmetric with what we have in our string
classes.

Change-Id: I94c5b39b718ca2472f9ca645e7a42e4314636f67
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

2 files changed, 72 insertions, 0 deletions

diff --git a/src/corelib/tools/qlist.h b/src/corelib/tools/qlist.h
index 6a699aa197..3b9eb154ed 100644
--- a/src/corelib/tools/qlist.h
+++ b/src/corelib/tools/qlist.h
@@ -378,6 +378,29 @@ public:
     inline bool endsWith(const T &t) const { return !isEmpty() && last() == t; }
     QList<T> mid(qsizetype pos, qsizetype len = -1) const;
 
+    QList<T> first(qsizetype n) const
+    {
+        Q_ASSERT(size_t(n) <= size_t(size()));
+        return QList<T>(begin(), begin() + n);
+    }
+    QList<T> last(qsizetype n) const
+    {
+        Q_ASSERT(size_t(n) <= size_t(size()));
+        return QList<T>(end() - n, end());
+    }
+    QList<T> sliced(qsizetype pos) const
+    {
+        Q_ASSERT(size_t(pos) <= size_t(size()));
+        return QList<T>(begin() + pos, end());
+    }
+    QList<T> sliced(qsizetype pos, qsizetype n) const
+    {
+        Q_ASSERT(size_t(pos) <= size_t(size()));
+        Q_ASSERT(n >= 0);
+        Q_ASSERT(pos + n <= size());
+        return QList<T>(begin() + pos, begin() + pos + n);
+    }
+
     T value(qsizetype i) const { return value(i, T()); }
     T value(qsizetype i, const T &defaultValue) const;
 
diff --git a/src/corelib/tools/qlist.qdoc b/src/corelib/tools/qlist.qdoc
index 550663ed0e..047c418469 100644
--- a/src/corelib/tools/qlist.qdoc
+++ b/src/corelib/tools/qlist.qdoc
@@ -202,6 +202,55 @@
     are included.
 */
 
+/*!
+    \fn template <typename T> QList<T> QList<T>::first(qsizetype n) const
+    \since 6.0
+
+    Returns a sub-list that contains the first \a n elements
+    of this list.
+
+    \note The behavior is undefined when \a n < 0 or \a n > size().
+
+    \sa last(), sliced()
+*/
+
+/*!
+    \fn template <typename T> QList<T> QList<T>::last(qsizetype n) const
+    \since 6.0
+
+    Returns a sub-list that contains the last \a n elements of this list.
+
+    \note The behavior is undefined when \a n < 0 or \a n > size().
+
+    \sa first(), sliced()
+*/
+
+/*!
+    \fn template <typename T> QList<T> QList<T>::sliced(qsizetype pos, qsizetype n) const
+    \since 6.0
+
+    Returns a sub-list that contains \a n elements of this list,
+    starting at position \a pos.
+
+    \note The behavior is undefined when \a pos < 0, \a n < 0,
+    or \a pos + \a n > size().
+
+    \sa first(), last()
+*/
+
+/*!
+    \fn template <typename T> QList<T> QList<T>::sliced(qsizetype pos) const
+    \since 6.0
+    \overload
+
+    Returns a sub-list that contains the elements of this list starting at
+    position \a pos and extending to its end.
+
+    \note The behavior is undefined when \a pos < 0 or \a pos > size().
+
+    \sa first(), last()
+*/
+
 
 /*! \fn template <typename T> QList<T>::QList()