error[E0015]: cannot call non-const fn `Box::::new` in statics --> $DIR/static-mut-not-constant.rs:1:28 | LL | static mut a: Box = Box::new(3); | ^^^^^^^^^^^ | = note: calls in statics are limited to constant functions, tuple structs and tuple variants = note: consider wrapping this expression in `Lazy::new(|| ...)` from the `once_cell` crate: https://crates.io/crates/once_cell error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0015`.