blob: b4efee7d6040fa75433c92032914442e398f3128 (
plain)
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
28
29
30
31
32
33
34
35
36
37
38
|
#![allow(dead_code)]
// Get<T> is covariant in T
trait Get<T> {
fn get(&self) -> T;
}
struct Cloner<T:Clone> {
t: T
}
impl<T:Clone> Get<T> for Cloner<T> {
fn get(&self) -> T {
self.t.clone()
}
}
fn get<'a, G>(get: &G) -> i32
where G : Get<&'a i32>
{
// This fails to type-check because, without variance, we can't
// use `G : Get<&'a i32>` as evidence that `G : Get<&'b i32>`,
// even if `'a : 'b`.
pick(get, &22) //~ ERROR explicit lifetime required in the type of `get` [E0621]
}
fn pick<'b, G>(get: &'b G, if_odd: &'b i32) -> i32
where G : Get<&'b i32>
{
let v = *get.get();
if v % 2 != 0 { v } else { *if_odd }
}
fn main() {
let x = Cloner { t: &23 };
let y = get(&x);
assert_eq!(y, 23);
}
|
