Rust – 从 trait 方法返回 trait 对象时无法推断出合适的生命周期

我正在try 制作类似于不可变字典特性的东西，可以在不影响以前版本的情况下添加新项目(引用)并使用它.最小示例:

#[derive(Clone)]
pub struct SetOfValues<'a> {
    value: Vec<&'a i32>,
}

pub trait TheSetAccessor<'b> {
    fn with_additional_values(&self, new_set: Vec<&'b i32>) -> Box<dyn TheSetAccessor<'b>>;
    fn get_from_set(&self, index: usize) -> &i32;
}

impl<'a, 'b : 'a> TheSetAccessor<'b> for SetOfValues<'a> {
    fn with_additional_values(&self, new_set: Vec<&'b i32>) -> Box<dyn TheSetAccessor<'b>> {
        Box::new(SetOfValues { value: new_set } )
    }

    fn get_from_set(&self, index: usize) -> &i32 {
        self.value[index]
    }
}

fn usage() {
    let a = 0;
    let set = SetOfValues {
        value: vec![&a]
    };

    // ...

    let b = 1;
    let extended_set = set.with_additional_values(vec![&a, &b]);

    // ...

    let got_b = extended_set.get_from_set(1);
}

错误消息如下:

error[E0495]: cannot infer an appropriate lifetime for lifetime parameter `'a` due to conflicting requirements
  --> src/test.rs:13:18
   |
13 |         Box::new(SetOfValues { value: new_set } )
   |                  ^^^^^^^^^^^
   |
note: first, the lifetime cannot outlive the lifetime `'b` as defined here...
  --> src/test.rs:11:10
   |
11 | impl<'a, 'b : 'a> TheSetAccessor<'b> for SetOfValues<'a> {
   |          ^^
note: ...so that the expression is assignable
  --> src/test.rs:13:39
   |
13 |         Box::new(SetOfValues { value: new_set } )
   |                                       ^^^^^^^
   = note: expected `Vec<&i32>`
              found `Vec<&'b i32>`
   = note: but, the lifetime must be valid for the static lifetime...
note: ...so that the types are compatible
  --> src/test.rs:13:9
   |
13 |         Box::new(SetOfValues { value: new_set } )
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
   = note: expected `Box<(dyn TheSetAccessor<'b> + 'static)>`
              found `Box<dyn TheSetAccessor<'b>>`

据我所知，新的值集应该具有传递向量('b)的生存期，但这部分

首先，生命周期 不能超过此处定义的生命周期 'b...

如我所见，这表明SetOfValues的新实例有另一个生存期("静态的")那应该比b活得更长.我不太明白我怎么能限制这一生.我该怎么做才能使此代码正常工作？