error[E0277]: expected a `FnOnce<({integer},)>` closure, found `unsafe fn(u8) -> NonZeroAndOneU8 {NonZeroAndOneU8}` --> $DIR/initializing-ranged-via-ctor.rs:9:34 | LL | println!("{:?}", Some(1).map(NonZeroAndOneU8).unwrap()); | --- ^^^^^^^^^^^^^^^ call the function in a closure: `|| unsafe { /* code */ }` | | | required by a bound introduced by this call | = help: the trait `FnOnce<({integer},)>` is not implemented for fn item `unsafe fn(u8) -> NonZeroAndOneU8 {NonZeroAndOneU8}` = note: unsafe function cannot be called generically without an unsafe block note: required by a bound in `Option::::map` --> $SRC_DIR/core/src/option.rs:LL:COL error: aborting due to previous error For more information about this error, try `rustc --explain E0277`.