error[E0308]: mismatched types --> $DIR/issue-11515.rs:9:33 | LL | let test = box Test { func: closure }; | ^^^^^^^ expected trait `std::ops::FnMut`, found trait `std::ops::Fn` | = note: expected type `std::boxed::Box<(dyn std::ops::FnMut() + 'static)>` found type `std::boxed::Box<(dyn std::ops::Fn() + 'static)>` error: aborting due to previous error For more information about this error, try `rustc --explain E0308`.