error[E0106]: missing lifetime specifier --> $DIR/issue-19707.rs:3:28 | LL | type Foo = fn(&u8, &u8) -> &u8; | --- --- ^ 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 type lifetime-generic with a new `'a` lifetime | LL | type Foo = for<'a> fn(&'a u8, &'a u8) -> &'a u8; | +++++++ ++ ++ ++ help: consider introducing a named lifetime parameter | LL | type Foo<'a> = fn(&'a u8, &'a u8) -> &'a u8; | ++++ ++ ++ ++ error[E0106]: missing lifetime specifier --> $DIR/issue-19707.rs:5:27 | LL | fn bar &u8>(f: &F) {} | --- --- ^ 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 help: consider making the bound lifetime-generic with a new `'a` lifetime | LL | fn bar Fn(&'a u8, &'a u8) -> &'a u8>(f: &F) {} | +++++++ ++ ++ ++ help: consider introducing a named lifetime parameter | LL | fn bar<'a, F: Fn(&'a u8, &'a u8) -> &'a u8>(f: &F) {} | +++ ++ ++ ++ error: aborting due to 2 previous errors For more information about this error, try `rustc --explain E0106`.