trait MyTrait {
    fn render(&self);
    fn change(&mut self, pos: f32);
}

struct Object {
 pos: f32
}

impl Object {
    pub fn new() -> Object {
        Object{ pos: 0. }
    }
}

impl MyTrait for Object {
    fn render(&self) {
        println!("Func render from trait... ({})", self.pos);
    }
    fn change(&mut self, pos: f32) {
        self.pos = pos;
    }
}

struct Scene<T: MyTrait> {
    list: Vec<Box<T>>
}

impl<T: MyTrait> Scene<T> {
    pub fn new() -> Scene<T> {
        Scene{ list: vec![] }
    }

    pub fn add(&mut self, object: T) {
        let obj = Box::new(object);
        self.list.push(obj);
    }

    pub fn render_all(&self) {
        for obj in &self.list {
            obj.render();
        }
    }

    pub fn get_mut(&mut self) -> &mut Box<T> {
        unsafe { self.list.get_unchecked_mut(0) }
    }
}

fn main() {
    let mut scene = Scene::new();
    let object = Object::new();
    scene.add(object);
    scene.render_all();
    scene.get_mut().change(42.);
    scene.render_all();
    println!("End...");
}