#![allow(dead_code, deprecated, unused_variables, unused_mut)]
#![feature(try_trait_v2)]
use std::ops::Try;
fn make_question_mark_work() -> Option<()> {
    assert_eq!(Option::from_output(4) ?, 4);
    None
}
fn main() {
    assert_eq!(< Result < _, String > as Try >::from_output(3), Ok(3));
    assert_eq!(< Option < _ > as Try >::from_output(4), Some(4));
    assert_eq!(
        < std::ops::ControlFlow < String, _ > as Try >::from_output(5),
        std::ops::ControlFlow::Continue(5),
    );
    make_question_mark_work();
    let r = std::iter::empty().try_fold(4, |_, ()| -> Option<_> { unreachable!() });
    assert_eq!(r, Some(4));
}