Can you generically render Widgets?

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You can have I'm trying to have generically add widgets.
But that has proven difficult due to the signature of Widget::add :

    fn ui(self, ui: &mut Ui) -> Response;

dyn Widget are unsized, and they take self by value instead of by reference. Hence you cannot use dyn objects.
Is this intentional or just happenstance?
Any other method to generically render ui?

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pub trait Widget {
    fn render(&mut self, ui: &mut egui::Ui);
}

I just made another Trait to render UI element, feels as if this should be part of Egui, but I didn't RTFM.