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/qwizard.cpp b/src/widgets/dialogs/qwizard.cpp
index aa10f65389..53f947354c 100644
--- a/src/widgets/dialogs/qwizard.cpp
+++ b/src/widgets/dialogs/qwizard.cpp
@@ -850,9 +850,9 @@ void QWizardPrivate::switchToPage(int newId, Direction direction)
                 q->cleanupPage(oldId);
                 initialized.remove(oldId);
             }
-            Q_ASSERT(history.last() == oldId);
+            Q_ASSERT(history.constLast() == oldId);
             history.removeLast();
-            Q_ASSERT(history.last() == newId);
+            Q_ASSERT(history.constLast() == newId);
         }
     }