struct Theme {}

impl Theme {
    fn new() -> Theme {
        Theme {}
    }
    fn get_standard_font_size(&self) -> i32 {
        12
    }
}

struct WidgetObj {
    font_size: i32
}

impl Widget for WidgetObj {
    fn get_theme(&self) -> Theme {
        Theme::new()
    }

    fn get_internal_font_size(&self) -> i32 {
        self.font_size
    }
}

impl WidgetObj {
    fn new(font_size: i32) -> WidgetObj {
        WidgetObj {
            font_size: font_size
        }
    }
}

trait Widget {
    fn get_theme(&self) -> Theme;
    fn get_internal_font_size(&self) -> i32;
    fn get_actual_font_size(&self) -> i32 {
        if self.get_internal_font_size() < 0 {
            return self.get_theme().get_standard_font_size();
        } else {
            return self.get_internal_font_size();
        }
    }
}

fn main() {
    let w = WidgetObj::new(-1);
    println!("actual font_size: {}", w.get_actual_font_size());
    println!("internal font_size: {}", w.get_internal_font_size());
}