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
39
|
// Tests that a non-const default impl can be specialized by a const trait impl,
// but that the default impl cannot be used in a const context.
// run-pass
#![feature(const_trait_impl)]
#![feature(min_specialization)]
#[const_trait]
trait Value {
fn value() -> u32;
}
const fn get_value<T: ~const Value>() -> u32 {
T::value()
}
impl<T> Value for T {
default fn value() -> u32 {
println!("You can't do that (constly)");
0
}
}
struct FortyTwo;
impl const Value for FortyTwo {
fn value() -> u32 {
42
}
}
fn main() {
let zero = get_value::<()>();
assert_eq!(zero, 0);
const FORTY_TWO: u32 = get_value::<FortyTwo>();
assert_eq!(FORTY_TWO, 42);
}
|
