use std::iter::Iterator;

type Iterable = Vec<String>;

struct Collection {
    items: Vec<Iterable>,
}

impl Collection {
    fn new() -> Self {
        Collection {
            items: Vec::new(),
        }
    }

    fn insert(&mut self, item: Iterable) {
        self.items.push(item);
    }

    fn iter(&self) -> CollectionIter {
        CollectionIter::new(self)
    }
}

struct CollectionIter;

impl CollectionIter {
    fn new(c: &Collection) -> Self {
        CollectionIter {}
    }
}

impl Iterator for CollectionIter {
    type Item = String;

    fn next(&mut self) -> Option<Self::Item> {
        None
    }
}

fn main() {
    let item1 = vec!["a".to_string(), "b".to_string(), "c".to_string()];
    let item2 = vec!["d".to_string(), "e".to_string(), "f".to_string()];
    let item3 = vec!["g".to_string(), "h".to_string(), "i".to_string()];

    let mut collection = Collection::new();
    collection.insert(item1);
    collection.insert(item2);
    collection.insert(item3);

    // Should print:
    //     0: a
    //     0: b
    //     0: c
    //     1: d
    //     1: e
    //     1: f
    //     2: g
    //     2: h
    //     2: i
    for i in collection.iter() {
        println!("{}", i);
    }
}