Doc: use const& in foreach when applicable.

Const reference are slightly faster than doing a copy of the object
on each iteration.

Lead by example by having this pattern right in our documentation

1 files changed, 2 insertions, 2 deletions

diff --git a/doc/src/snippets/qlistview-dnd/model.cpp b/doc/src/snippets/qlistview-dnd/model.cpp
index d310c03..bca71ee 100644
--- a/doc/src/snippets/qlistview-dnd/model.cpp
+++ b/doc/src/snippets/qlistview-dnd/model.cpp
@@ -109,7 +109,7 @@ bool DragDropListModel::dropMimeData(const QMimeData *data,
 
 //! [6]
     insertRows(beginRow, rows, QModelIndex());
-    foreach (QString text, newItems) {
+    foreach (const QString &text, newItems) {
         QModelIndex idx = index(beginRow, 0, QModelIndex());
         setData(idx, text);
         beginRow++;
@@ -139,7 +139,7 @@ QMimeData *DragDropListModel::mimeData(const QModelIndexList &indexes) const
 
     QDataStream stream(&encodedData, QIODevice::WriteOnly);
 
-    foreach (QModelIndex index, indexes) {
+    foreach (const QModelIndex &index, indexes) {
         if (index.isValid()) {
             QString text = data(index, Qt::DisplayRole).toString();
             stream << text;