QtWidgets: prevent detach attempts from first()/etc. use [dialogs, kernel, util, widgets]

The algorithm used was:
- If possible, just declare the container const
- Otherwise, for first()/last(), use constFirst()/constLast()
  and for front()/back(), to not destroy the use of the STL
  API subset, use qAsConst()

Did some caching of function returns here and there, and
converted one 0 to nullptr as a drive-by.

Also saves almost 4KiB in text size on optimized GCC 4.9
Linux AMD64 builds.

Change-Id: I04b7bfd68dc85c22de247cb65a310e1cbbca1e8c
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Lars Knoll <lars.knoll@theqtcompany.com>
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>

1 files changed, 2 insertions, 2 deletions

diff --git a/src/widgets/dialogs/qsidebar.cpp b/src/widgets/dialogs/qsidebar.cpp
index 2e884e238d..1b1eb6472e 100644
--- a/src/widgets/dialogs/qsidebar.cpp
+++ b/src/widgets/dialogs/qsidebar.cpp
@@ -127,7 +127,7 @@ QMimeData *QUrlModel::mimeData(const QModelIndexList &indexes) const
 */
 bool QUrlModel::canDrop(QDragEnterEvent *event)
 {
-    if (!event->mimeData()->formats().contains(mimeTypes().first()))
+    if (!event->mimeData()->formats().contains(mimeTypes().constFirst()))
         return false;
 
     const QList<QUrl> list = event->mimeData()->urls();
@@ -145,7 +145,7 @@ bool QUrlModel::canDrop(QDragEnterEvent *event)
 bool QUrlModel::dropMimeData(const QMimeData *data, Qt::DropAction action,
                                  int row, int column, const QModelIndex &parent)
 {
-    if (!data->formats().contains(mimeTypes().first()))
+    if (!data->formats().contains(mimeTypes().constFirst()))
         return false;
     Q_UNUSED(action);
     Q_UNUSED(column);