raw_pointers.rs

struct Item {
    list: *mut List,
}

impl Item {
    fn new(list: *mut List) -> Self {
        Item { list: list }
    }
}

impl Item {
    fn get_len(&self) -> usize {
        unsafe {
            (*self.list).values.len()
        }
    }
}

struct List {
    values: Vec<Item>,
}

impl List {
    fn new() -> Self {
        List { values: Vec::new() }
    }

    fn push(&mut self) -> &Item {
        let item = Item::new(self);
        self.values.push(item);
        &self.values.last().unwrap()
    }

    fn with_first() -> Self {
        let mut list = List::new();
        list.push();
        list
    }
}

fn main() {
    let mut list = List::new();
    list.push();
    assert_eq!(list.values[0].get_len(), 1);


    let list = List::with_first();
    assert_eq!(list.values[0].get_len(), 1);
}