trait MyTrait<I, O> {
    type MyType;

    fn my_method(&self);

    fn dummy(_: std::marker::PhantomData<(I, O)>) {}
}

impl<F, I, O> MyTrait<I, O> for F
where
    F: Fn(I) -> O,
{
    type MyType = F::Output;

    fn my_method(&self) {}


}

fn main() {}