2.8.3特征对象章节的代码示例的建议

[elimsc]

章节2.8.3 特征对象

文中给了段代码来说明特征对象，代码如下

trait Draw {
    fn draw(&self) -> String; 
}

impl Draw for u8 {
    fn draw(&self) -> String {
        format!("u8: {}", *self) 
    } 
}

impl Draw for f64 {
    fn draw(&self) -> String {
        format!("f64: {}", *self) 
    } 
}

fn draw1(x: Box<dyn Draw>) {
    x.draw();
}

fn draw2(x: &dyn Draw) {
    x.draw();
}

fn main() {
    let x = 1.1f64;
    // do_something(&x);
    let y = 8u8;

    draw1(Box::new(x));
    draw1(Box::new(y));
    draw2(&x);
    draw2(&y);
}

但我读到这里的时候其实是比较困惑的，因为这里没有体现为什么需要特征对象，这里只是陈述了如何创建特征对象以及如何接收特征对象，我觉得改为如下的例子的话会更好的说明为什么需要它

trait Draw {
    fn draw(&self) -> String;
}

impl Draw for u8 {
    fn draw(&self) -> String {
        format!("u8 {}", *self)
    }
}

impl Draw for f64 {
    fn draw(&self) -> String {
        format!("f64 {}", *self)
    }
}

fn draw1(components: Vec<Box<dyn Draw>>) {
    for c in components.iter() {
        println!("{}", c.draw());
    }
}

fn draw2(components: Vec<&dyn Draw>) {
    for c in components.iter() {
        println!("{}", c.draw());
    }
}

fn draw3(components: Vec<impl Draw>) {
    for c in components.iter() {
        println!("{}", c.draw());
    }
}

fn main() {
    let x = 1.1_f64;
    let y = 8_u8;

    draw1(vec![Box::new(x), Box::new(y)]);
    draw2(vec![&x, &y]);
    // draw3(vec![x, y]); // don't work
}