Inherent async fn returning Self treats type's lifetime parameters as 'static #61949
Description
rustc 1.37.0-nightly (2887008e0 2019-06-12) and playground's 2019-06-17 b25ee644971a168287ee
#![feature(async_await)] pub struct Foo<'a> { pub bar: &'a i32, } impl<'a> Foo<'a> { pub async fn new(bar: &'a i32) -> Self { Foo { bar } } }error[E0495]: cannot infer an appropriate lifetime due to conflicting requirements --> src/lib.rs:8:22 | 8 | pub async fn new(bar: &'a i32) -> Self { | ^^^ | note: first, the lifetime cannot outlive the lifetime 'a as defined on the impl at 7:6... --> src/lib.rs:7:6 | 7 | impl<'a> Foo<'a> { | ^^ = note: ...so that the expression is assignable: expected &i32 found &'a i32 = note: but, the lifetime must be valid for the static lifetime... = note: ...so that the types are compatible: expected Foo<'_> found Foo<'static> It works to either change the signature to take bar: &'static i32, or to change the body of the fn to use a static borrow like bar: &5. So the compiler really does want the function to return a Foo<'static>, even though Self is a Foo<'a>
The workaround is to not use Self:
- pub async fn new(bar: &'a i32) -> Self { + pub async fn new(bar: &'a i32) -> Foo<'a> {Mentoring notes: See notes here on Zulip.