= note: `impl Trait` as a return type requires that all the returned values must have the same type
= help: you can instead return a trait object using `Box<dyn Foo>`
= note: for information on `impl Trait`, see <https://doc.rust-lang.org/book/ch10-02-traits.html#returning-types-that-implement-traits>
= 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>