1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
|
// regression test of https://github.com/rust-lang/rust/pull/133572#issuecomment-2543007164
// see also the test for UniqueArc in variance-uniquearc.rs
//
// inline comments explain how this code *would* compile if UniqueRc was still covariant
#![feature(unique_rc_arc)]
use std::rc::UniqueRc;
fn extend_lifetime<'a, 'b>(x: &'a str) -> &'b str {
let r = UniqueRc::new(""); // UniqueRc<&'static str>
let w = UniqueRc::downgrade(&r); // Weak<&'static str>
let mut r = r; // [IF COVARIANT]: ==>> UniqueRc<&'a str>
*r = x; // assign the &'a str
let _r = UniqueRc::into_rc(r); // Rc<&'a str>, but we only care to activate the weak
let r = w.upgrade().unwrap(); // Rc<&'static str>
*r // &'static str, coerces to &'b str
//~^ ERROR lifetime may not live long enough
}
fn main() {
let s = String::from("Hello World!");
let r = extend_lifetime(&s);
println!("{r}");
drop(s);
println!("{r}");
}
|
