为什么不能满足这种更高种类的、与寿命相关的类型特征？

Question

trait A<'self_>: 'self_ {
    type I;
}
trait AMut
where
    Self: for<'self_> A<'self_>,
    for<'self_> <Self as A<'self_>>::I: 'static,
{
    fn mutate_self(&mut self);
}

fn foo<X>(x: &mut X)
where
    X: 'static + for<'a> A<'a> + AMut,
    for<'a> <X as A<'a>>::I: 'static,
{
    x.mutate_self();
}

操场

此错误与

error[E0280]: the requirement `for<'self_> <Self as A<'self_>>::I: 'static` is not satisfied
  --> src/lib.rs:4:1
   |
4  |   trait AMut
   |   ^     ---- required by a bound in this
   |  _|
   | |
5  | | where
6  | |     Self: for<'self_> A<'self_>,
7  | |     for<'self_> <Self as A<'self_>>::I: 'static,
   | |                                         ------- required by this bound in `AMut`
8  | | {
9  | |     fn mutate_self(&mut self);
10 | | }
   | |_^

error[E0280]: the requirement `for<'self_> <X as A<'self_>>::I: 'static` is not satisfied
  --> src/lib.rs:14:34
   |
4  | trait AMut
   |       ---- required by a bound in this
...
7  |     for<'self_> <Self as A<'self_>>::I: 'static,
   |                                         ------- required by this bound in `AMut`
...
14 |     X: 'static + for<'a> A<'a> + AMut,
   |                                  ^^^^

我本以为第15行的界限会满足第7行的界限。我错过了什么？

Answer 1

你试过这样吗？

trait A<'self_>: 'self_ {
    type I;
}
trait AMut<'a>
where
    Self: A<'a>,
    <Self as A<'a>>::I: 'static,
{
    fn mutate_self(&mut self);
}

fn foo<X>(x: &mut X)
where
    X: 'static + for<'a> A<'a> + for<'a> AMut<'a>,
    for<'a> <X as A<'a>>::I: 'static,
{
    x.mutate_self();
}