Code shared from the Rust Playground

playground.rs

trait Widget {
    fn base_widget(&mut self) -> &mut dyn Widget;

    fn render(&mut self) {
        self.base_widget().render();
    }
}

struct BaseWidget;

impl Widget for BaseWidget {
    fn base_widget(&mut self) -> &mut dyn Widget {
        unreachable!("Attempt to base on self")
    }
    fn render(&mut self) {
        println!("BaseWidget Render");
    }
}

struct Button {
    base_widget: BaseWidget
}

impl Widget for Button {
    fn base_widget(&mut self) -> &mut dyn Widget {
        &mut self.base_widget
    }
}

fn main() {
    let mut widget = Button {
        base_widget: BaseWidget
    };
    widget.render();
}