src/doc/book/listings/ch19-advanced-features/no-listing-18-returns-closure/output.txt

$ cargo build
   Compiling functions-example v0.1.0 (file:///projects/functions-example)
error[E0277]: the size for values of type `(dyn std::ops::Fn(i32) -> i32 + 'static)` cannot be known at compilation time
 --> src/lib.rs:1:25
  |
1 | fn returns_closure() -> dyn Fn(i32) -> i32 {
  |                         ^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
  |
  = help: the trait `std::marker::Sized` is not implemented for `(dyn std::ops::Fn(i32) -> i32 + 'static)`
  = note: to learn more, visit <https://doc.rust-lang.org/book/ch19-04-advanced-types.html#dynamically-sized-types-and-the-sized-trait>
  = note: the return type of a function must have a statically known size

error[E0308]: mismatched types
 --> src/lib.rs:2:5
  |
1 | fn returns_closure() -> dyn Fn(i32) -> i32 {
  |                         ------------------ expected `(dyn std::ops::Fn(i32) -> i32 + 'static)` because of return type
2 |     |x| x + 1
  |     ^^^^^^^^^ expected trait `std::ops::Fn`, found closure
  |
  = note: expected trait object `(dyn std::ops::Fn(i32) -> i32 + 'static)`
                  found closure `[closure@src/lib.rs:2:5: 2:14]`

error: aborting due to 2 previous errors

Some errors have detailed explanations: E0277, E0308.
For more information about an error, try `rustc --explain E0277`.
error: could not compile `functions-example`.

To learn more, run the command again with --verbose.