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, 3 insertions, 3 deletions

diff --git a/src/widgets/widgets/qtabbar.cpp b/src/widgets/widgets/qtabbar.cpp
index cf485974f6..ba3fc2fcd7 100644
--- a/src/widgets/widgets/qtabbar.cpp
+++ b/src/widgets/widgets/qtabbar.cpp
@@ -590,7 +590,7 @@ QRect QTabBarPrivate::normalizedScrollRect(int index)
         }
 
         bool tearTopVisible = index != 0 && topEdge != -scrollOffset;
-        bool tearBottomVisible = index != tabList.size() - 1 && bottomEdge != tabList.last().rect.bottom() + 1 - scrollOffset;
+        bool tearBottomVisible = index != tabList.size() - 1 && bottomEdge != tabList.constLast().rect.bottom() + 1 - scrollOffset;
         if (tearTopVisible && !tearLeftRect.isNull())
             topEdge = tearLeftRect.bottom() + 1;
         if (tearBottomVisible && !tearRightRect.isNull())
@@ -621,7 +621,7 @@ QRect QTabBarPrivate::normalizedScrollRect(int index)
         }
 
         bool tearLeftVisible = index != 0 && leftEdge != -scrollOffset;
-        bool tearRightVisible = index != tabList.size() - 1 && rightEdge != tabList.last().rect.right() + 1 - scrollOffset;
+        bool tearRightVisible = index != tabList.size() - 1 && rightEdge != tabList.constLast().rect.right() + 1 - scrollOffset;
         if (tearLeftVisible && !tearLeftRect.isNull())
             leftEdge = tearLeftRect.right() + 1;
         if (tearRightVisible && !tearRightRect.isNull())
@@ -642,7 +642,7 @@ void QTabBarPrivate::makeVisible(int index)
     const bool horiz = !verticalTabs(shape);
     const int tabStart = horiz ? tabRect.left() : tabRect.top();
     const int tabEnd = horiz ? tabRect.right() : tabRect.bottom();
-    const int lastTabEnd = horiz ? tabList.last().rect.right() : tabList.last().rect.bottom();
+    const int lastTabEnd = horiz ? tabList.constLast().rect.right() : tabList.constLast().rect.bottom();
     const QRect scrollRect = normalizedScrollRect(index);
     const int scrolledTabBarStart = qMax(1, scrollRect.left() + scrollOffset);
     const int scrolledTabBarEnd = qMin(lastTabEnd - 1, scrollRect.right() + scrollOffset);