如何指定特征参数的类型?

How do I specify types for a trait parameter?

我正在尝试将特征用作我的结构中的字段:

pub trait Scene {
    type Renderer;

    fn update(&mut self);
    fn render(&mut self, r: &mut Self::Renderer);
}

struct Example {
    active_scene: *mut Scene,
}

当我尝试使用它时,出现错误:

error[E0191]: the value of the associated type `Renderer` (from the trait `Scene`) must be specified
 --> src/lib.rs:9:24
  |
9 |     active_scene: *mut Scene,
  |                        ^^^^^ missing associated type `Renderer` value

如何在字段中指定类型?有什么明显的我想念的吗?

语法如下:

Scene<Renderer = YourRenderer>