error[E0308]: mismatched types --> $DIR/call-boxed.rs:4:9 | LL | let mut x = 1i32; | ---- expected due to this value LL | let y = Box::new(|| 1); | -- the found closure LL | x = y; | ^ expected `i32`, found `Box<{closure@call-boxed.rs:3:22}>` | = note: expected type `i32` found struct `Box<{closure@$DIR/call-boxed.rs:3:22: 3:24}>` help: use parentheses to call this closure | LL | x = y(); | ++ error: aborting due to 1 previous error For more information about this error, try `rustc --explain E0308`.