1error[E0658]: parenthetical notation is only stable when used with `Fn`-family traits 2 --> $DIR/unboxed-closure-feature-gate.rs:13:20 3 | 4LL | let x: Box<dyn Foo(isize)>; 5 | ^^^^^^^^^^ 6 | 7 = note: see issue #29625 <https://github.com/rust-lang/rust/issues/29625> for more information 8 = help: add `#![feature(unboxed_closures)]` to the crate attributes to enable 9 10error: aborting due to previous error 11 12For more information about this error, try `rustc --explain E0658`. 13