// run-pass #![feature(unsized_fn_params)] use std::ops; use std::ops::Index; pub struct A; impl ops::Index for A { type Output = (); fn index(&self, _: str) -> &Self::Output { &() } } impl ops::IndexMut for A { fn index_mut(&mut self, _: str) -> &mut Self::Output { panic!() } } fn main() { let a = A {}; let s = String::new().into_boxed_str(); assert_eq!(&(), a.index(*s)); }