I'm having some lifetime issues I don't fully understand when working with a function that takes in an AsRef<str> and returns a Future with a 'static lifetime. Here is a minimal example of the general situation:
extern crate futures;
extern crate tokio;
use futures::{Future, future::ok};
fn make_future(_s: impl AsRef<str>) -> impl Future<Item = (), Error = ()> + 'static {
// Do stuff...
ok(())
}
fn main() {
let test = "test".to_string();
tokio::run(make_future(&test));
}
Playground link: Rust Playground
In this example, you can imagine that make_future() is a function that takes an argument of some type that implements AsRef<str>, calls .as_ref() on it, and based on the borrowed value constructs some Future which does not hold any references (and is thus 'static).
The example above fails to compile:
error[E0597]: `test` does not live long enough
--> src/main.rs:13:29
|
13 | tokio::run(make_future(&test));
| ^^^^ borrowed value does not live long enough
14 | }
| - borrowed value only lives until here
|
= note: borrowed value must be valid for the static lifetime...
I don't understand why I'm getting this error, because it doesn't seem like the function signature should place any bounds on the lifetime of _s (the only trait bound present is AsRef<str>. I figured this might have something to do with lifetime elision, but changing the type of _s to &str causes the code to compile successfully.
Does anyone know what is going on here?