error[E0658]: parenthetical notation is only stable when used with `Fn`-family traits (see issue #29625) | |
--> $DIR/unboxed-closure-feature-gate.rs:13:16 | |
| | |
LL | let x: Box<Foo(isize)>; | |
| ^^^^^^^^^^ | |
| | |
= help: add #![feature(unboxed_closures)] to the crate attributes to enable | |
error: aborting due to previous error | |
For more information about this error, try `rustc --explain E0658`. |