QHeaderView: apply small optimization in recalcSectionStartPos()

The loop in recalcSectionStartPos() calls QVector<>::constEnd() after
every iteration which is not needed since the vector stays constant.
Therefore use the new for loop syntax from c++11 so constEnd() is only
called once which gives a small speedup, noticeable with large section
counts.

Change-Id: If318eec10c9ce234004a9922409fbdbc6409f2f8
Reviewed-by: Samuel Gaist <samuel.gaist@idiap.ch>
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>
Reviewed-by: Luca Beldi <v.ronin@yahoo.it>

1 files changed, 3 insertions, 3 deletions

diff --git a/src/widgets/itemviews/qheaderview.cpp b/src/widgets/itemviews/qheaderview.cpp
index 3396a91dc5..2f276a7a8c 100644
--- a/src/widgets/itemviews/qheaderview.cpp
+++ b/src/widgets/itemviews/qheaderview.cpp
@@ -3877,9 +3877,9 @@ void QHeaderViewPrivate::updateDefaultSectionSizeFromStyle()
 void QHeaderViewPrivate::recalcSectionStartPos() const // linear (but fast)
 {
     int pixelpos = 0;
-    for (QVector<SectionItem>::const_iterator i = sectionItems.constBegin(); i != sectionItems.constEnd(); ++i) {
-        i->calculated_startpos = pixelpos; // write into const mutable
-        pixelpos += i->size;
+    for (const SectionItem &i : sectionItems) {
+        i.calculated_startpos = pixelpos; // write into const mutable
+        pixelpos += i.size;
     }
     sectionStartposRecalc = false;
 }