QSizePolicy::ControlTypes QLayoutItem::controlTypes() const
{
    // ### Qt 5: This function should probably be virtual instead
    if (const QWidget *widget = const_cast<QLayoutItem*>(this)->widget()) {
        return widget->sizePolicy().controlType();
...
    /*
      ### Qt 4.0:
      If the layout is expanding, we make the widget expanding, even if
      its own size policy isn't expanding. This behavior should be
      reconsidered.
    */