use std::{convert::Infallible, future::Future, marker::PhantomData};

trait Trait {}

struct MyFn<'a, F, Fut>(F, PhantomData<&'a Fut>);

impl<'a, F, Fut> MyFn<'a, F, Fut>
where
    F: Fn(&'a u8, &'a u16) -> Fut,
    Fut: Future<Output = Result<(), Infallible>>
{
    pub fn new(f: F) -> Self {
        MyFn(f, PhantomData)
    }
}

impl<'a, F, Fut> Trait for MyFn<'a, F, Fut>
where
    F: Fn(&'a u8, &'a u16) -> Fut,
    Fut: Future<Output = Result<(), Infallible>>,
{
}

async fn lol(_: &u8, _: &u16) -> Result<(), Infallible> {
    Ok(())
}

fn check<T: Trait>(_: T) {}

pub fn check2() {
    check(MyFn::new(lol))
}