error[E0658]: mutable references are not allowed in constant functions --> $DIR/mutable_borrow.rs:3:13 | LL | let b = &mut a; | ^^^^^^ | = note: see issue #57349 for more information = help: add `#![feature(const_mut_refs)]` to the crate attributes to enable error[E0658]: mutable references are not allowed in constant functions --> $DIR/mutable_borrow.rs:12:17 | LL | let b = &mut a; | ^^^^^^ | = note: see issue #57349 for more information = help: add `#![feature(const_mut_refs)]` to the crate attributes to enable error: aborting due to 2 previous errors For more information about this error, try `rustc --explain E0658`.