error[E0277]: the trait bound `fn() -> Foo: Bar` is not satisfied --> $DIR/call-on-unimplemented-fn-ptr.rs:10:15 | LL | needs_bar(f); | --------- ^ the trait `Bar` is not implemented for `fn() -> Foo` | | | required by a bound introduced by this call | note: required by a bound in `needs_bar` --> $DIR/call-on-unimplemented-fn-ptr.rs:7:17 | LL | fn needs_bar(_: T) {} | ^^^ required by this bound in `needs_bar` help: use parentheses to call this function pointer | LL | needs_bar(f()); | ++ error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0277`.