fn make_iter(first: &First) -> Box<dyn Iterator<Item=String> + '_> {
    Box::new(first.make_objects().flat_map(|second| {
        second.iter()
            .filter(|third| third.as_str() != "t2")
            .flat_map(|third| {
                vec![
                    format!("{}.A", third),
                    format!("{}.B", third),
                ].into_iter()
            })
            .chain(
                vec![
                    format!("{}.A", second.name()),
                    format!("{}.B", second.name()),
                ].into_iter()
            )
    }))
}

pub fn main() {
    let first = First{};
    for i in make_iter(&first) {
        println!("{}", i);
    }
}

struct First {}

impl First {
    fn make_objects(&self) -> Box<dyn Iterator<Item=Second> + '_> {
        Box::new(vec![
            Second::new("s1".to_string()),
            Second::new("s2".to_string()),
            Second::new("s3".to_string()),
        ].into_iter())
    }
}

struct Second {
    name: String,
    objects: Vec<String>,
}

impl Second {
    fn new(name: String) -> Second {
        Second {
            name,
            objects: vec!["t1".to_string(), "t2".to_string(), "t3".to_string()],
        }
    }

    fn name(&self) -> &str {
        &self.name
    }

    fn iter(&self) -> Box<dyn Iterator<Item=&String> + '_> {
        Box::new(self.objects.iter())
    }
}

error[E0597]: `second` does not live long enough
  --> src/main.rs:4:9
   |
4  |         second.iter()
   |         ^^^^^^ borrowed value does not live long enough
...
18 |     }))
   |     - `second` dropped here while still borrowed

error: aborting due to previous error