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, 1 insertions, 1 deletions

diff --git a/src/widgets/dialogs/qfilesystemmodel.cpp b/src/widgets/dialogs/qfilesystemmodel.cpp
index bfa40317eb..c72761f2ae 100644
--- a/src/widgets/dialogs/qfilesystemmodel.cpp
+++ b/src/widgets/dialogs/qfilesystemmodel.cpp
@@ -374,7 +374,7 @@ QFileSystemModelPrivate::QFileSystemNode *QFileSystemModelPrivate::node(const QS
     QModelIndex index = QModelIndex(); // start with "My Computer"
 #if defined(Q_OS_WIN) && !defined(Q_OS_WINCE)
     if (absolutePath.startsWith(QLatin1String("//"))) { // UNC path
-        QString host = QLatin1String("\\\\") + pathElements.first();
+        QString host = QLatin1String("\\\\") + pathElements.constFirst();
         if (absolutePath == QDir::fromNativeSeparators(host))
             absolutePath.append(QLatin1Char('/'));
         if (longPath.endsWith(QLatin1Char('/')) && !absolutePath.endsWith(QLatin1Char('/')))