Unify all mid() functions in QtBase.

Up to now, Qt had at least 3 different implementations of the mid().
Only QString::mid implementation was not crashing on edge cases and
was protected against overflows, therefore I picked that one as the
base implementation, even if it has weird semantics for an invalid
input.

As a side effect QVector::mid was slightly optimized to not detach in
all cases (which follows current QList behavior). Documentation of
QVector::mid and QList::mid was updated to not mention "copy of data"
which could suggest that the mid() result is detached.

QStringRef::mid was fixed and now it follows general Qt behavior, by
returning a null value for a null input.

Change-Id: Ie9ff5d98372bd193d66508e6dd92b6ed1180ad9b
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 11 insertions, 3 deletions

diff --git a/src/corelib/tools/qlist.h b/src/corelib/tools/qlist.h
index 9e4ba70908..4c52c22300 100644
--- a/src/corelib/tools/qlist.h
+++ b/src/corelib/tools/qlist.h
@@ -45,6 +45,7 @@
 #include <QtCore/qalgorithms.h>
 #include <QtCore/qiterator.h>
 #include <QtCore/qrefcount.h>
+#include <QtCore/qarraydata.h>
 
 #include <iterator>
 #include <list>
@@ -646,10 +647,17 @@ inline void QList<T>::move(int from, int to)
 template<typename T>
 Q_OUTOFLINE_TEMPLATE QList<T> QList<T>::mid(int pos, int alength) const
 {
-    if (alength < 0 || pos > size() - alength)
-        alength = size() - pos;
-    if (pos == 0 && alength == size())
+    using namespace QtPrivate;
+    switch (QContainerImplHelper::mid(size(), &pos, &alength)) {
+    case QContainerImplHelper::Null:
+    case QContainerImplHelper::Empty:
+        return QList<T>();
+    case QContainerImplHelper::Full:
         return *this;
+    case QContainerImplHelper::Subset:
+        break;
+    }
+
     QList<T> cpy;
     if (alength <= 0)
         return cpy;