How can I write a generic matcher?

5 
// Errors if you use this alias
// type Input<'a, This> = <This as HigherMatcher<'a>>::Input;

interesting.. but that’s a soundness issue, actually!!

use std::marker::PhantomData;

trait HigherMatcher<'a, _Outlives = &'a Self> {
    type Input: Copy;
}

type Input<'a, This> = <This as HigherMatcher<'a>>::Input;

impl HigherMatcher<'_> for &'_ () {
    type Input = ();
}
fn foo<'a>(y: &'a str) -> &'static str {
    let x: PhantomData<Input<'static, &'a ()>> = PhantomData;
    bar::<'a>(y, x)
}
fn bar<'a>(y: &'a str, x: PhantomData<Input<'static, &'a ()>>) -> &'static str
where
    'a: 'a,
{
    baz::<'a>(y, x)
}
fn baz<'a>(y: &'a str, x: PhantomData<<&'a () as HigherMatcher<'static>>::Input>) -> &'static str
where
    'a: 'a,
{
    qux(y)
}
fn qux(y: &'static str) -> &'static str {
    y
}

fn main() {
    let x = String::from("Hello World!");
    let y = foo(&x);
    drop(x);
    println!("{}", y);
}