src/test/ui/never_type/issue-51506.rs

   1 #![feature(never_type, specialization)]
   2 #![allow(incomplete_features)]
   3
   4 use std::iter::{self, Empty};
   5
   6 trait Trait {
   7     type Out: Iterator<Item = u32>;
   8
   9     fn f(&self) -> Option<Self::Out>;
  10 }
  11
  12 impl<T> Trait for T {
  13     default type Out = !; //~ ERROR: `!` is not an iterator
  14
  15     default fn f(&self) -> Option<Self::Out> {
  16         None
  17     }
  18 }
  19
  20 struct X;
  21
  22 impl Trait for X {
  23     type Out = Empty<u32>;
  24
  25     fn f(&self) -> Option<Self::Out> {
  26         Some(iter::empty())
  27     }
  28 }
  29
  30 fn f<T: Trait>(a: T) {
  31     if let Some(iter) = a.f() {
  32         println!("Some");
  33         for x in iter {
  34             println!("x = {}", x);
  35         }
  36     }
  37 }
  38
  39 pub fn main() {
  40     f(10);
  41 }