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#![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);
}
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