Lifetime bound vs lifetime parameter

1

In the following code:

trait Tr {}

struct S<'t, T>(&'t T);

impl<'t, T> Tr for S<'t, T> {}

fn f<'a>(s: impl Tr + 'a) {

}

fn main() {
    let x = 1i32;
    let s = S(&x);
    f(s);
}

What's the relation between 't and 'a?

As far as I know, S<'t, ...> means that the lifetime of instance of S<'t, ...> (let's say it's 's) cannot outlive 't.

According to Rust-lifetime-misconceptions, s: Tr + 'a indicates that s can be one of the following:

  • a reference with exact lifetime 'a
  • an owned type whose lifetime outlives 'a with or without any lifetime parameters

so we can conclude that 't outlives 's outlives 'a.

Is my understanding correct?

2

The meaning of impl Tr + 'a is that all lifetimes annotated on the type must be larger than or equal to 'a. So we have 't larger than or equal to 'a in this case.

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