Reduce allocations and time spent creating delegates by half

src/timeline/DelegateChooser.cpp

@@ -53,6 +53,7 @@ DelegateChooser::setRoleValue(const QVariant &value)
 {
     if (value != roleValue_) {
         roleValue_ = value;
+        if (isComponentComplete())
             recalcChild();
         emit roleValueChanged();
     }
@@ -96,8 +97,8 @@ void
 DelegateChooser::recalcChild()
 {
     for (const auto choice : qAsConst(choices_)) {
-        auto choiceValue = choice->roleValue();
-        if (!roleValue_.isValid() || !choiceValue.isValid() || choiceValue == roleValue_) {
+        const auto &choiceValue = choice->roleValueRef();
+        if (choiceValue == roleValue_ || (!choiceValue.isValid() && !roleValue_.isValid())) {
             if (child_) {
                 child_->setParentItem(nullptr);
                 child_ = nullptr;

src/timeline/DelegateChooser.h

@@ -25,10 +25,11 @@ public:
     Q_PROPERTY(QVariant roleValue READ roleValue WRITE setRoleValue NOTIFY roleValueChanged)
     Q_PROPERTY(QQmlComponent *delegate READ delegate WRITE setDelegate NOTIFY delegateChanged)
 
-    QQmlComponent *delegate() const;
+    [[nodiscard]] QQmlComponent *delegate() const;
     void setDelegate(QQmlComponent *delegate);
 
-    QVariant roleValue() const;
+    [[nodiscard]] QVariant roleValue() const;
+    [[nodiscard]] const QVariant &roleValueRef() const { return roleValue_; }
     void setRoleValue(const QVariant &value);
 
 signals:
@@ -53,10 +54,10 @@ public:
 
     QQmlListProperty<DelegateChoice> choices();
 
-    QVariant roleValue() const;
+    [[nodiscard]] QVariant roleValue() const;
     void setRoleValue(const QVariant &value);
 
-    QQuickItem *child() const { return child_; }
+    [[nodiscard]] QQuickItem *child() const { return child_; }
 
     void recalcChild();
     void componentComplete() override;