error[E0277]: the size for values of type `(dyn Fn() -> Fut + 'static)` cannot be known at compilation time --> $DIR/dont-elaborate-non-self.rs:7:11 | LL | fn f(a: dyn F) {} | ^ doesn't have a size known at compile-time | = help: the trait `Sized` is not implemented for `(dyn Fn() -> Fut + 'static)` = help: unsized fn params are gated as an unstable feature help: you can use `impl Trait` as the argument type | LL | fn f(a: impl F) {} | ~~~~ help: function arguments must have a statically known size, borrowed types always have a known size | LL | fn f(a: &dyn F) {} | + error: aborting due to previous error For more information about this error, try `rustc --explain E0277`.