type Src = Vec<u8>;
type Dst = String;

trait Trait<T> {
    type Assoc;
}

// Effectively: type Alias = dyn Trait<i32, Assoc = Src>
struct Dummy;
trait DummyTrait {
    type DummyAssoc: ?Sized;
}
impl DummyTrait for Dummy {
    type DummyAssoc = dyn Trait<i32, Assoc = Src>;
}
type Alias = <Dummy as DummyTrait>::DummyAssoc;

impl<T> Trait<T> for Alias {
    type Assoc = Dst;
}

fn foo<T>(x: <Alias as Trait<T>>::Assoc) -> Dst {
    x
}

fn bar(x: Src) -> Dst {
    foo::<i32>(x)
}

fn main() {
    let x: Vec<u8> = vec![102, 117, 110, 115, 111, 117, 110, 100];
    let y: String = bar(x);
    println!("{y}");
}