必须指定关联类型 `item` 的值（来自 trait `Draw`）

Question

pub trait Draw {
    type item;

    fn draw(&self);
}

pub struct Screen {
    pub comps: Vec<Box<dyn Draw>>,
}

impl Screen {
    pub fn run(&self) {
        for comp in self.comps.iter() {
            comp.draw();
        }
    }
}

我收到此错误消息：

error[E0191]: the value of the associated type `item` (from trait `Draw`) must be specified
  --> src/main.rs:12:28
   |
6  |     type item;
   |     ---------- `item` defined here
...
12 |     pub comps: Vec<Box<dyn Draw>>,
   |                            ^^^^ help: specify the associated type: `Draw<item = Type>`

我该如何解决？

Answer 1

指定trait对象vec时需要指定item的具体类型

即

pub struct Screen {
    pub comps: Vec<Box<dyn Draw<item = i64>>>,
}

必须指定关联类型 `item` 的值（来自 trait `Draw`）

the value of the associated type `item` (from trait `Draw`) must be specified

rust