1 Return type involving a trait did not require `'static` lifetime.
3 Erroneous code examples:
8 fn foo(x: &i32) -> impl Debug { // error!
12 fn bar(x: &i32) -> Box<dyn Debug> { // error!
17 Add `'static` requirement to fix them:
20 # use std::fmt::Debug;
21 fn foo(x: &'static i32) -> impl Debug + 'static { // ok!
25 fn bar(x: &'static i32) -> Box<dyn Debug + 'static> { // ok!
30 Both [`dyn Trait`] and [`impl Trait`] in return types have an implicit
31 `'static` requirement, meaning that the value implementing them that is being
32 returned has to be either a `'static` borrow or an owned value.
34 In order to change the requirement from `'static` to be a lifetime derived from
35 its arguments, you can add an explicit bound, either to an anonymous lifetime
36 `'_` or some appropriate named lifetime.
39 # use std::fmt::Debug;
40 fn foo(x: &i32) -> impl Debug + '_ {
43 fn bar(x: &i32) -> Box<dyn Debug + '_> {
48 These are equivalent to the following explicit lifetime annotations:
51 # use std::fmt::Debug;
52 fn foo<'a>(x: &'a i32) -> impl Debug + 'a {
55 fn bar<'a>(x: &'a i32) -> Box<dyn Debug + 'a> {
60 [`dyn Trait`]: https://doc.rust-lang.org/book/ch17-02-trait-objects.html#using-trait-objects-that-allow-for-values-of-different-types
61 [`impl Trait`]: https://doc.rust-lang.org/book/ch10-02-traits.html#returning-types-that-implement-traits