fn fun(x: i32) -> i32 {
    x + 1
}

fn main()
{
    let v = vec![Some(1), None, Some(2), Some(3), Some(4), None, None, Some(5)];

    let it = v.iter().filter(|x| x.is_some()).map(|x| fun(x.unwrap()));
    //let it = v.iter().flat_map(|x| x).map(fun);

    let v3: Vec<_> = it.collect();
    println!("{:?}", v3);

}