Rust 无法克隆 Vec> 因为无法将 Trait 制成对象

我想克隆一个盒状特征的载体.

好吧，然后我试着用Clone作为超级trait ，但这只会导致标题中的错误.我找不到解决办法.

以下是最低限度的工作实现(或者不工作，因为我无法克隆)

#![allow(dead_code, unused_macros)]
use std::fmt::Debug;

trait MusicElement: Debug + Clone {
    fn duration(&self) -> f32;
}

#[derive(Debug, Clone)]
struct Note<'a> {
    name: &'a str,
    duration: f32,
}

impl<'a> MusicElement for Note<'a> {
    fn duration(&self) -> f32 {
        self.duration
    }
}

#[derive(Debug, Clone)]
struct Pause {
    duration: f32,
}

impl MusicElement for Pause {
    fn duration(&self) -> f32 {
        self.duration
    }
}

#[derive(Debug, Clone)]
struct Sequence {
    elements: Vec<Box<MusicElement>>,
}

impl MusicElement for Sequence {
    fn duration(&self) -> f32 {
        self.elements.iter().map(|e| e.duration()).sum()
    }
}

fn main() {
    let a4 = |dur| Box::new(Note { name: "a4", duration: dur });
    let seq = Sequence { elements: vec![a4(0.25), a4(0.25), a4(0.5)] };
    println!("{:?}", seq);
    let seq2 = seq.clone();
    println!("{:?}", seq2);
}

出现以下错误:

error[E0038]: the trait `MusicElement` cannot be made into an object
  --> src/main.rs:33:5
   |
33 |     elements: Vec<Box<MusicElement>>,
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `MusicElement` cannot be made into an object
   |
   = note: the trait cannot require that `Self : Sized`

这里有一个link to the playground，便于代码运行.

我也试着把Sequence中的elements向量变成Vec<Box<MusicElement + Clone>>，但也没用.

我还没有在网上找到任何有用的解决方案，所以我的问题是:如何使代码可克隆？