Widgets: use QStringRef to optimize memory allocation

Replace substring functions that return QString with
corresponding functions that return QStringRef where
it's possible.

Create QString from QStringRef only where necessary.

Change-Id: Id1c39093199519f2794b11560c2c0ded2d52b928
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>

8 files changed, 24 insertions, 20 deletions

diff --git a/src/widgets/dialogs/qfiledialog.cpp b/src/widgets/dialogs/qfiledialog.cpp
index c4ed72edc3..d9b6dc05bf 100644
--- a/src/widgets/dialogs/qfiledialog.cpp
+++ b/src/widgets/dialogs/qfiledialog.cpp
@@ -3823,11 +3823,11 @@ QString QFileDialogPrivate::getEnvironmentVariable(const QString &string)
 {
 #ifdef Q_OS_UNIX
     if (string.size() > 1 && string.startsWith(QLatin1Char('$'))) {
-        return QString::fromLocal8Bit(qgetenv(string.mid(1).toLatin1().constData()));
+        return QString::fromLocal8Bit(qgetenv(string.midRef(1).toLatin1().constData()));
     }
 #else
     if (string.size() > 2 && string.startsWith(QLatin1Char('%')) && string.endsWith(QLatin1Char('%'))) {
-        return QString::fromLocal8Bit(qgetenv(string.mid(1, string.size() - 2).toLatin1().constData()));
+        return QString::fromLocal8Bit(qgetenv(string.midRef(1, string.size() - 2).toLatin1().constData()));
     }
 #endif
     return string;
diff --git a/src/widgets/styles/qfusionstyle.cpp b/src/widgets/styles/qfusionstyle.cpp
index b15b9701d9..5b6e47e2c6 100644
--- a/src/widgets/styles/qfusionstyle.cpp
+++ b/src/widgets/styles/qfusionstyle.cpp
@@ -1649,7 +1649,7 @@ void QFusionStyle::drawControl(ControlElement element, const QStyleOption *optio
 
             QRect textRect(xpos, y + windowsItemVMargin, w - xm - windowsRightBorder - tab + 1, h - 2 * windowsItemVMargin);
             QRect vTextRect = visualRect(opt->direction, menuitem->rect, textRect);
-            QString s = menuitem->text;
+            QStringRef s(&menuitem->text);
             if (!s.isEmpty()) {                     // draw text
                 p->save();
                 int t = s.indexOf(QLatin1Char('\t'));
@@ -1660,12 +1660,13 @@ void QFusionStyle::drawControl(ControlElement element, const QStyleOption *optio
                 if (t >= 0) {
                     QRect vShortcutRect = visualRect(opt->direction, menuitem->rect,
                                                      QRect(textRect.topRight(), QPoint(menuitem->rect.right(), textRect.bottom())));
+                    const QString textToDraw = s.mid(t + 1).toString();
                     if (dis && !act && proxy()->styleHint(SH_EtchDisabledText, option, widget)) {
                         p->setPen(menuitem->palette.light().color());
-                        p->drawText(vShortcutRect.adjusted(1, 1, 1, 1), text_flags, s.mid(t + 1));
+                        p->drawText(vShortcutRect.adjusted(1, 1, 1, 1), text_flags, textToDraw);
                         p->setPen(discol);
                     }
-                    p->drawText(vShortcutRect, text_flags, s.mid(t + 1));
+                    p->drawText(vShortcutRect, text_flags, textToDraw);
                     s = s.left(t);
                 }
                 QFont font = menuitem->font;
@@ -1680,12 +1681,13 @@ void QFusionStyle::drawControl(ControlElement element, const QStyleOption *optio
                     font.setBold(true);
 
                 p->setFont(font);
+                const QString textToDraw = s.left(t).toString();
                 if (dis && !act && proxy()->styleHint(SH_EtchDisabledText, option, widget)) {
                     p->setPen(menuitem->palette.light().color());
-                    p->drawText(vTextRect.adjusted(1, 1, 1, 1), text_flags, s.left(t));
+                    p->drawText(vTextRect.adjusted(1, 1, 1, 1), text_flags, textToDraw);
                     p->setPen(discol);
                 }
-                p->drawText(vTextRect, text_flags, s.left(t));
+                p->drawText(vTextRect, text_flags, textToDraw);
                 p->restore();
             }
 
diff --git a/src/widgets/styles/qstylesheetstyle.cpp b/src/widgets/styles/qstylesheetstyle.cpp
index 053820e459..44555c3058 100644
--- a/src/widgets/styles/qstylesheetstyle.cpp
+++ b/src/widgets/styles/qstylesheetstyle.cpp
@@ -3679,7 +3679,7 @@ void QStyleSheetStyle::drawControl(ControlElement ce, const QStyleOption *opt, Q
 
                 QRect textRect = subRule.contentsRect(opt->rect);
                 textRect.setWidth(textRect.width() - mi.tabWidth);
-                QString s = mi.text;
+                QStringRef s(&mi.text);
                 p->setPen(mi.palette.buttonText().color());
                 if (!s.isEmpty()) {
                     int text_flags = Qt::AlignLeft | Qt::AlignVCenter | Qt::TextShowMnemonic | Qt::TextDontClip | Qt::TextSingleLine;
@@ -3689,10 +3689,10 @@ void QStyleSheetStyle::drawControl(ControlElement ce, const QStyleOption *opt, Q
                     if (t >= 0) {
                         QRect vShortcutRect = visualRect(opt->direction, mi.rect,
                             QRect(textRect.topRight(), QPoint(mi.rect.right(), textRect.bottom())));
-                        p->drawText(vShortcutRect, text_flags, s.mid(t + 1));
+                        p->drawText(vShortcutRect, text_flags, s.mid(t + 1).toString());
                         s = s.left(t);
                     }
-                    p->drawText(textRect, text_flags, s.left(t));
+                    p->drawText(textRect, text_flags, s.left(t).toString());
                 }
 
                 if (mi.menuItemType == QStyleOptionMenuItem::SubMenu) {// draw sub menu arrow
diff --git a/src/widgets/styles/qwindowsstyle.cpp b/src/widgets/styles/qwindowsstyle.cpp
index 36aa312ce8..2ef227762b 100644
--- a/src/widgets/styles/qwindowsstyle.cpp
+++ b/src/widgets/styles/qwindowsstyle.cpp
@@ -1198,7 +1198,7 @@ void QWindowsStyle::drawControl(ControlElement ce, const QStyleOption *opt, QPai
             QRect textRect(xpos, y + QWindowsStylePrivate::windowsItemVMargin,
                            w - xm - QWindowsStylePrivate::windowsRightBorder - tab + 1, h - 2 * QWindowsStylePrivate::windowsItemVMargin);
             QRect vTextRect = visualRect(opt->direction, menuitem->rect, textRect);
-            QString s = menuitem->text;
+            QStringRef s(&menuitem->text);
             if (!s.isEmpty()) {                     // draw text
                 p->save();
                 int t = s.indexOf(QLatin1Char('\t'));
@@ -1209,24 +1209,26 @@ void QWindowsStyle::drawControl(ControlElement ce, const QStyleOption *opt, QPai
                 if (t >= 0) {
                     QRect vShortcutRect = visualRect(opt->direction, menuitem->rect,
                         QRect(textRect.topRight(), QPoint(menuitem->rect.right(), textRect.bottom())));
+                    const QString textToDraw = s.mid(t + 1).toString();
                     if (dis && !act && proxy()->styleHint(SH_EtchDisabledText, opt, widget)) {
                         p->setPen(menuitem->palette.light().color());
-                        p->drawText(vShortcutRect.adjusted(1,1,1,1), text_flags, s.mid(t + 1));
+                        p->drawText(vShortcutRect.adjusted(1, 1, 1, 1), text_flags, textToDraw);
                         p->setPen(discol);
                     }
-                    p->drawText(vShortcutRect, text_flags, s.mid(t + 1));
+                    p->drawText(vShortcutRect, text_flags, textToDraw);
                     s = s.left(t);
                 }
                 QFont font = menuitem->font;
                 if (menuitem->menuItemType == QStyleOptionMenuItem::DefaultItem)
                     font.setBold(true);
                 p->setFont(font);
+                const QString textToDraw = s.left(t).toString();
                 if (dis && !act && proxy()->styleHint(SH_EtchDisabledText, opt, widget)) {
                     p->setPen(menuitem->palette.light().color());
-                    p->drawText(vTextRect.adjusted(1,1,1,1), text_flags, s.left(t));
+                    p->drawText(vTextRect.adjusted(1, 1, 1, 1), text_flags, textToDraw);
                     p->setPen(discol);
                 }
-                p->drawText(vTextRect, text_flags, s.left(t));
+                p->drawText(vTextRect, text_flags, textToDraw);
                 p->restore();
             }
             if (menuitem->menuItemType == QStyleOptionMenuItem::SubMenu) {// draw sub menu arrow
diff --git a/src/widgets/widgets/qcalendarwidget.cpp b/src/widgets/widgets/qcalendarwidget.cpp
index 66e4a89fe9..caeabb660b 100644
--- a/src/widgets/widgets/qcalendarwidget.cpp
+++ b/src/widgets/widgets/qcalendarwidget.cpp
@@ -554,7 +554,7 @@ void QCalendarDateValidator::setFormat(const QString &format)
     bool quoting = false;
     QString separator;
     while (pos < format.size()) {
-        QString mid = format.mid(pos);
+        const QStringRef mid = format.midRef(pos);
         int offset = 1;
 
         if (mid.startsWith(quote)) {
diff --git a/src/widgets/widgets/qlineedit_p.cpp b/src/widgets/widgets/qlineedit_p.cpp
index 6ff40e9c50..3d8a854753 100644
--- a/src/widgets/widgets/qlineedit_p.cpp
+++ b/src/widgets/widgets/qlineedit_p.cpp
@@ -97,7 +97,7 @@ void QLineEditPrivate::_q_completionHighlighted(const QString &newText)
     } else {
         int c = control->cursor();
         QString text = control->text();
-        q->setText(text.left(c) + newText.mid(c));
+        q->setText(text.leftRef(c) + newText.midRef(c));
         control->moveCursor(control->end(), false);
 #ifndef Q_OS_ANDROID
         const bool mark = true;
diff --git a/src/widgets/widgets/qwidgetlinecontrol.cpp b/src/widgets/widgets/qwidgetlinecontrol.cpp
index a77794df8a..7fab2c1de5 100644
--- a/src/widgets/widgets/qwidgetlinecontrol.cpp
+++ b/src/widgets/widgets/qwidgetlinecontrol.cpp
@@ -1180,14 +1180,14 @@ QString QWidgetLineControl::maskString(uint pos, const QString &str, bool clear)
                     int n = findInMask(i, true, true, str[(int)strIndex]);
                     if (n != -1) {
                         if (str.length() != 1 || i == 0 || (i > 0 && (!m_maskData[i-1].separator || m_maskData[i-1].maskChar != str[(int)strIndex]))) {
-                            s += fill.mid(i, n-i+1);
+                            s += fill.midRef(i, n - i + 1);
                             i = n + 1; // update i to find + 1
                         }
                     } else {
                         // search for valid m_blank if not
                         n = findInMask(i, true, false, str[(int)strIndex]);
                         if (n != -1) {
-                            s += fill.mid(i, n-i);
+                            s += fill.midRef(i, n - i);
                             switch (m_maskData[n].caseMode) {
                             case MaskInputData::Upper:
                                 s += str[(int)strIndex].toUpper();
diff --git a/src/widgets/widgets/qwidgettextcontrol.cpp b/src/widgets/widgets/qwidgettextcontrol.cpp
index dfb1f865dc..af6d879661 100644
--- a/src/widgets/widgets/qwidgettextcontrol.cpp
+++ b/src/widgets/widgets/qwidgettextcontrol.cpp
@@ -2123,7 +2123,7 @@ QVariant QWidgetTextControl::inputMethodQuery(Qt::InputMethodQuery property, QVa
             tmpCursor.movePosition(QTextCursor::NextBlock);
             --numBlocks;
         }
-        result += block.text().mid(0,localPos);
+        result += block.text().midRef(0, localPos);
         return QVariant(result);
     }
     default: