error[E0308]: mismatched types --> $DIR/suggest-box.rs:4:47 | LL | let _x: Box Result<(), ()>> = || { | _____________-------------------------------___^ | | | | | expected due to this LL | | Err(())?; LL | | Ok(()) LL | | }; | |_____^ expected `Box Result<(), ()>>`, found closure | = note: expected struct `Box Result<(), ()>>` found closure `{closure@$DIR/suggest-box.rs:4:47: 4:49}` = note: for more on the distinction between the stack and the heap, read https://doc.rust-lang.org/book/ch15-01-box.html, https://doc.rust-lang.org/rust-by-example/std/box.html, and https://doc.rust-lang.org/std/boxed/index.html help: store this in the heap by calling `Box::new` | LL ~ let _x: Box Result<(), ()>> = Box::new(|| { LL | Err(())?; LL | Ok(()) LL ~ }); | error: aborting due to previous error For more information about this error, try `rustc --explain E0308`.