error[E0106]: missing lifetime specifier --> $DIR/unboxed-closure-sugar-lifetime-elision.rs:26:39 | LL | let _: dyn Foo(&isize, &usize) -> &usize; | ------ ------ ^ expected named lifetime parameter | = help: this function's return type contains a borrowed value, but the signature does not say whether it is borrowed from argument 1 or argument 2 = note: for more information on higher-ranked polymorphism, visit https://doc.rust-lang.org/nomicon/hrtb.html help: consider making the bound lifetime-generic with a new `'a` lifetime | LL | let _: dyn for<'a> Foo(&'a isize, &'a usize) -> &'a usize; | +++++++ ++ ++ ++ help: consider introducing a named lifetime parameter | LL ~ fn main<'a>() { LL | eq::< dyn for<'a> Foo<(&'a isize,), Output=&'a isize>, ... LL | LL ~ let _: dyn Foo(&'a isize, &'a usize) -> &'a usize; | error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0106`.