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#![feature(never_type, specialization)]
#![allow(incomplete_features)]
use std::iter::{self, Empty};
trait Trait {
type Out: Iterator<Item = u32>;
fn f(&self) -> Option<Self::Out>;
}
impl<T> Trait for T {
default type Out = !; //~ ERROR: `!` is not an iterator
default fn f(&self) -> Option<Self::Out> {
None
}
}
struct X;
impl Trait for X {
type Out = Empty<u32>;
fn f(&self) -> Option<Self::Out> {
Some(iter::empty())
}
}
fn f<T: Trait>(a: T) {
if let Some(iter) = a.f() {
println!("Some");
for x in iter {
println!("x = {}", x);
}
}
}
pub fn main() {
f(10);
}
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