E0495 - Error codes index
Description: Book listing all Rust error codes

# Error code E0495

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

A lifetime cannot be determined in the given situation.

Erroneous code example:

    #![allow(unused)]
    fn main() {
    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`:

    #![allow(unused)]
    fn main() {
    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`:

    #![allow(unused)]
    fn main() {
    fn transmute_lifetime<'a, T>(t: &'a (T,)) -> &'a T {
        match (&t,) { // ok!
            ((u,),) => u,
        }
    }
    }