error[E0608]: cannot index into a value of type `()` --> $DIR/issue-40861.rs:4:7 | LL | ()[f(&[1.0])]; | ^^^^^^^^^^^ | = help: to access tuple elements, use tuple indexing syntax (e.g., `tuple.0`) error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0608`.