src/test/ui/suggestions/as-ref.rs

struct Foo;
fn takes_ref(_: &Foo) {}

fn main() {
  let ref opt = Some(Foo);
  opt.map(|arg| takes_ref(arg));
  //~^ ERROR mismatched types [E0308]
  opt.and_then(|arg| Some(takes_ref(arg)));
  //~^ ERROR mismatched types [E0308]
  let ref opt: Result<_, ()> = Ok(Foo);
  opt.map(|arg| takes_ref(arg));
  //~^ ERROR mismatched types [E0308]
  opt.and_then(|arg| Ok(takes_ref(arg)));
  //~^ ERROR mismatched types [E0308]
  let x: &Option<usize> = &Some(3);
  let y: Option<&usize> = x;
  //~^ ERROR mismatched types [E0308]
  let x: &Result<usize, usize> = &Ok(3);
  let y: Result<&usize, &usize> = x;
  //~^ ERROR mismatched types [E0308]
  // note: do not suggest because of `E: usize`
  let x: &Result<usize, usize> = &Ok(3);
  let y: Result<&usize, usize> = x;
  //~^ ERROR mismatched types [E0308]
}