#![feature(generic_associated_types)]

trait X {
    type Y<'a>;
}

fn f(x: Box<dyn X<Y<'a>=&'a ()>>) {}
// or perhaps:
// fn f(x: Box<dyn for<'a> X<Y<'a>=&'a ()>>) {}

fn g<T: X<Y<'a>=&'a ()>>() {}