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/qfileinfogatherer.cpp b/src/widgets/dialogs/qfileinfogatherer.cpp
index 48ae5f1fc4..b20db8fc7c 100644
--- a/src/widgets/dialogs/qfileinfogatherer.cpp
+++ b/src/widgets/dialogs/qfileinfogatherer.cpp
@@ -217,9 +217,9 @@ void QFileInfoGatherer::run()
             condition.wait(&mutex);
         if (abort.load())
             return;
-        const QString thisPath = path.front();
+        const QString thisPath = qAsConst(path).front();
         path.pop_front();
-        const QStringList thisList = files.front();
+        const QStringList thisList = qAsConst(files).front();
         files.pop_front();
         locker.unlock();