关于rust：参数类型的寿命可能不够长(带有线程)

Parameter type may not live long enough (with threads)

这类似于Parameter type是否可能寿命不长？，但是我对解决方案的解释似乎无效。我最初的简化测试用例是：

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use std::fmt::Debug;
use std::thread;

trait HasFeet: Debug + Send + Sync + Clone {}

#[derive(Debug, Clone)]
struct Person;

impl HasFeet for Person {}

#[derive(Debug, Copy, Clone)]
struct Cordwainer<A: HasFeet> {
shoes_for: A,
}

impl<A: HasFeet> Cordwainer<A> {
fn make_shoes(&self) {
let cloned = self.shoes_for.clone();
thread::spawn(move || {
println!("making shoes for = {:?}", cloned);
});
}
}

这给了我错误：

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error[E0310]: the parameter type `A` may not live long enough
--> src/main.rs:19:9
|
16 | impl<A: HasFeet> Cordwainer<A> {
| -- help: consider adding an explicit lifetime bound `A: 'static`...
...
19 | thread::spawn(move || {
| ^^^^^^^^^^^^^
|
note: ...so that the type `[closure@src/main.rs:19:23: 21:10 cloned:A]` will meet its required lifetime bounds
--> src/main.rs:19:9
|
19 | thread::spawn(move || {
| ^^^^^^^^^^^^^

我没有制作A 'static，而是为HasFeet特性添加了显式寿命：

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use std::fmt::Debug;
use std::thread;

trait HasFeet<'a>: 'a + Send + Sync + Debug {}

#[derive(Debug, Copy, Clone)]
struct Person;

impl<'a> HasFeet<'a> for Person {}

struct Cordwainer<'a, A: HasFeet<'a>> {
shoes_for: A,
}

impl<'a, A: HasFeet<'a>> Cordwainer<'a, A> {
fn make_shoes(&self) {
let cloned = self.shoes_for.clone();
thread::spawn(move || {
println!("making shoes for = {:?}", cloned);
})
}
}

现在这给了我错误：

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error[E0392]: parameter `'a` is never used
--> src/main.rs:11:19
|
11 | struct Cordwainer<'a, A: HasFeet<'a>> {
| ^^ unused type parameter
|
= help: consider removing `'a` or using a marker such as `std::marker::PhantomData`

我认为'a用作HasFeet特性的生命周期参数。我在这里做错了什么？