1 error[E0308]: `if` and `else` have incompatible types
2 --> $DIR/box-instead-of-dyn-fn.rs:10:9
5 LL | | move || println!("{a}")
6 | | -----------------------
8 | | the expected closure
9 | | expected because of this
11 LL | | Box::new(move || println!("{}", b))
12 | | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected closure, found struct `Box`
15 | |_____- `if` and `else` have incompatible types
17 = note: expected closure `[closure@$DIR/box-instead-of-dyn-fn.rs:8:9: 8:16]`
18 found struct `Box<[closure@$DIR/box-instead-of-dyn-fn.rs:10:18: 10:25]>`
20 error[E0746]: return type cannot have an unboxed trait object
21 --> $DIR/box-instead-of-dyn-fn.rs:5:56
23 LL | fn print_on_or_the_other<'a>(a: i32, b: &'a String) -> dyn Fn() + 'a {
24 | ^^^^^^^^^^^^^ doesn't have a size known at compile-time
26 = note: for information on trait objects, see <https://doc.rust-lang.org/book/ch17-02-trait-objects.html#using-trait-objects-that-allow-for-values-of-different-types>
27 = note: if all the returned values were of the same type you could use `impl Fn() + 'a` as the return type
28 = note: for information on `impl Trait`, see <https://doc.rust-lang.org/book/ch10-02-traits.html#returning-types-that-implement-traits>
29 = note: you can create a new `enum` with a variant for each returned type
30 help: return a boxed trait object instead
32 LL | fn print_on_or_the_other<'a>(a: i32, b: &'a String) -> Box<dyn Fn() + 'a> {
34 help: ... and box this value
36 LL | Box::new(move || println!("{a}"))
39 error: aborting due to 2 previous errors
41 Some errors have detailed explanations: E0308, E0746.
42 For more information about an error, try `rustc --explain E0308`.