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// 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);
}
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