error[E0308]: `if` and `else` have incompatible types --> $DIR/box-instead-of-dyn-fn.rs:10:9 | LL | / if a % 2 == 0 { LL | | move || println!("{a}") | | ----------------------- | | | | | the expected closure | | expected because of this LL | | } else { LL | | Box::new(move || println!("{}", b)) | | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected closure, found struct `Box` LL | | LL | | } | |_____- `if` and `else` have incompatible types | = note: expected closure `[closure@$DIR/box-instead-of-dyn-fn.rs:8:9: 8:32]` found struct `Box<[closure@$DIR/box-instead-of-dyn-fn.rs:10:18: 10:43]>` error[E0746]: return type cannot have an unboxed trait object --> $DIR/box-instead-of-dyn-fn.rs:5:56 | LL | fn print_on_or_the_other<'a>(a: i32, b: &'a String) -> dyn Fn() + 'a { | ^^^^^^^^^^^^^ doesn't have a size known at compile-time | = note: for information on trait objects, see = note: if all the returned values were of the same type you could use `impl Fn() + 'a` as the return type = note: for information on `impl Trait`, see = note: you can create a new `enum` with a variant for each returned type help: return a boxed trait object instead | LL | fn print_on_or_the_other<'a>(a: i32, b: &'a String) -> Box { | ++++ + help: ... and box this value | LL | Box::new(move || println!("{a}")) | +++++++++ + error: aborting due to 2 previous errors Some errors have detailed explanations: E0308, E0746. For more information about an error, try `rustc --explain E0308`.