Rust error E0495: #### Note: this error code is no longer emitted by the compiler

The compiler team's explanation

Note: this error code is no longer emitted by the compiler.

A lifetime cannot be determined in the given situation.

Erroneous code example:

fn transmute_lifetime<'a, 'b, T>(t: &'a (T,)) -> &'b T {
    match (&t,) { // error!
        ((u,),) => u,
    }
}

let y = Box::new((42,));
let x = transmute_lifetime(&y);

In this code, you have two ways to solve this issue: 1. Enforce that 'a lives at least as long as 'b. 2. Use the same lifetime requirement for both input and output values.

So for the first solution, you can do it by replacing 'a with 'a: 'b:

fn transmute_lifetime<'a: 'b, 'b, T>(t: &'a (T,)) -> &'b T {
    match (&t,) { // ok!
        ((u,),) => u,
    }
}

In the second you can do it by simply removing 'b so they both use 'a:

fn transmute_lifetime<'a, T>(t: &'a (T,)) -> &'a T {
    match (&t,) { // ok!
        ((u,),) => u,
    }
}

From rustc --explain E0495 (1.99.0), part of the Rust project, MIT or Apache-2.0. Official page.