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, 10 insertions, 5 deletions

diff --git a/src/corelib/tools/qvector.h b/src/corelib/tools/qvector.h
index 0a32c96958..9692477e18 100644
--- a/src/corelib/tools/qvector.h
+++ b/src/corelib/tools/qvector.h
@@ -822,12 +822,17 @@ int QVector<T>::count(const T &t) const
 template <typename T>
 Q_OUTOFLINE_TEMPLATE QVector<T> QVector<T>::mid(int pos, int len) const
 {
-    if (len < 0)
-        len = size() - pos;
-    if (pos == 0 && len == size())
+    using namespace QtPrivate;
+    switch (QContainerImplHelper::mid(d->size, &pos, &len)) {
+    case QContainerImplHelper::Null:
+    case QContainerImplHelper::Empty:
+        return QVector<T>();
+    case QContainerImplHelper::Full:
         return *this;
-    if (pos + len > size())
-        len = size() - pos;
+    case QContainerImplHelper::Subset:
+        break;
+    }
+
     QVector<T> copy;
     copy.reserve(len);
     for (int i = pos; i < pos + len; ++i)