Understanding Rust Error E0760

Introduction to Rust Error E0760

Rust Error E0760 occurs when the return type of an async function or impl trait contains a projectionor or Self that references lifetimes from a parent scope. This error is due to a current limitation in Rust's compiler, which is anticipated to be resolved in future releases.

Incorrect code example

#![allow(unused)]
fn main() {
struct S<'a>(&'a i32);

impl<'a> S<'a> {
    async fn new(i: &'a i32) -> Self {
        S(&22)
    }
}
}

Explanation of the issue

In the above example, the async function 'new' tries to return 'Self'. However, 'Self' contains a lifetime parameter, which is not allowed. To fix this error, you need to explicitly specify the return type, including the lifetime parameter.

Correct code example

#![allow(unused)]
fn main() {
struct S<'a>(&'a i32);

impl<'a> S<'a> {
    async fn new(i: &'a i32) -> S<'a> {
        S(&22)
    }
}
}

Explanation of the solution

As shown above, the solution to Rust Error E0760 is to replace 'Self' with 'S<'a>'. This change ensures that the lifetime parameter is successfully included in the return type. It is worth noting that this limitation may be removed in future Rust updates, as indicated by issue-61949.

Conclusion

Rust Error E0760 is caused by a current limitation in Rust's async implementation. To resolve the error, explicitly return the struct type with the appropriate lifetime parameter, rather than using 'Self'. Be aware that this limitation might be lifted in future releases of Rust's compiler.