error[E0507]: cannot move out of `bar`, a captured variable in an `FnMut` closure --> $DIR/borrowck-move-by-capture.rs:9:29 | LL | let bar: Box<_> = Box::new(3); | --- captured outer variable LL | let _g = to_fn_mut(|| { | -- captured by this `FnMut` closure LL | let _h = to_fn_once(move || -> isize { *bar }); | ^^^^^^^^^^^^^^^^ ---- | | | | | variable moved due to use in closure | | move occurs because `bar` has type `Box`, which does not implement the `Copy` trait | `bar` is moved here error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0507`.