```rust pub fn f(_: &(ToString + 'static)) {} ``` This function is documented as: >  The parentheses are missing and the function would not compile without them: ``` error[E0178]: expected a path on the left-hand side of `+`, not `&ToString` --> src/main.rs:1:13 | 1 | pub fn f(_: &ToString + 'static) {} | ^^^^^^^^^^^^^^^^^^^ help: try adding parentheses: `&(ToString + 'static)` ```